NUCLEIC ACIDS AND POLYPEPTIDES OF INVERTEBRATE TWIK CHANNELS AND METHODS OF USE

Abstract: Tandem pore domain weak inward rectifying K<+> (TWIK) channel nucleic acids and proteins that have been isolated from <i>Drosophila melanogaster</i> and <i>Leptinotarsa</i> are described. The TWIK channel nucleic acids and proteins can be used to genetically modify metazoan invertebrate organisms, such as insects, coelomates, and pseudocoelomates, or cultured cells, resulting in TWIK channel expression or mis-expression. The genetically modified organisms or cells can be used in screening assays to identify candidate compounds which are potential pesticidal agents or therapeutics that interact with TWIK channel proteins. They can also be used in methods for studying TWIK channel activity and identifying other genes that modulate the function of, or interact with, the TWIK channel gene.

Description: NUCLEIC ACIDS AND POLYPEPTIDES OF INVERTEBRATE TWIK CHANNELS AND METHODS OF USE FIELD OF THE INVENTION The invention relates to novel invertebrate TWIK channel nucleic acid and polypeptide sequences and their uses in genetic screens and compound screening. BACKGROUND OF THE INVENTION Potassium channels are present in virtually all living cells, and are the most diverse class of ion channels. They conduct the flux of potassium ions through the membrane, and in doing so, are involved in the control of numerous cellular functions, such as neuronal firing, muscle contraction, volume regulation, cellular proliferation, and hormone secretion (Rudy, Neuroscience (1988) 25: 729-749; Hille in: ionic Channels in Excitable Membranes, 2nd Ed. (1992) Sinauer Associates, Inc., Sunderland, MA.). Two characteristic features of this class of channels are pore-forming (P) domains that have a conserved sequence motif, and at least two transmembrane (TM) domains. It is believed that four P domains contribute to the formation of a functional potassium-conducting pore (MacKinnon, Nature (1991) 350: 232-235; Yang et al., Neuron (1995) 15: 1441-1447; Doyle et al., Science (1998) 280: 69-77). There are three structural classes of potassium channels, based on their protein encoding subunits, and defined by the number of TM and P domains: 1) voltage-gated, Shaker-like outward rectifier K+ channels are characterized by the presence of six TM domains and one P domain; 2) inward rectifier, G-protein-coupled K+ channels are characterized by 2 TM domains and one P domain; and 3) tandem pore domain weak inward rectifying K+ (TWIK) channels, depicted in Fig. 1, are characterized by the presence of four TM domains and two P domains. The P domains of the TWIK channels are separated by the second and third TM domains. Although all members of this family have a conserved core region between the first and fourth TM domains, the-and C-terminal domains are quite diverse. The TWIK-related channels, TREK-1, TASK (also called cTBAK-1), and TRAAK exhibit the same overall structure, despite their low similarity at the amino acid level (Fink et al., EMBO J (1996) 15: 6854-6862; Duprat et al., EMBO J. (1997) 16: 5464-5471; Fink et al., EMBO J. (1998) 17: 3297-3308; Leonoudakis et al., J. Neurosci. (1998) 18: 868-877; Kim et al., Circ. Res. (1998) 82: 513-518). Some TWIK family members are known to dimerize through the presence of a disulfide bridge (Lesage et al., EMBO J. (1996) 15: 6400-6407), and seem to be involved in the generation and modulation of the resting potential of many cell types (Lesage and Lazdunski in: Potassium Ion Channels: Molecular Structure, Function, and Diseases (1998), Kurachi et al., eds., Academic Press, San Diego, CA). TWIK channels are widespread in mammals (Lesage et al., EMBO J. (1996) 15: 1004-1011; Chavez et al., J. Biol. Chem. (1999) 274: 7887-7892) and in Caenorhabditis elegans (hereinafter"C. elegans" ; Wei et al., Neuropharmacology (1996) 35: 805-829). To date, however, only one TWIK channel from Drosophila melanogaster has been reported (Goldstein et al., PNAS (1996) 93: 13256-13261; U. S. Pat. No. 5,559,026); and there have been no further reports of TWIK channels in other insect species. Pesticide development has traditionally focused on the chemical and physical properties of the pesticide itself, a relatively time-consuming and expensive process. As a consequence, efforts have been concentrated on the modification of pre-existing, well-validated compounds, rather than on the development of new pesticides. A promising alternative is to identify and validate biological targets against which potential ligands can be screened (Margolis and Duyk, Nature Biotech. (1998) 16: 311). Production of new compounds that are safer, selective, and more efficient can be implemented using target-based discovery approaches. Further, identifying molecular diversity addressing such targets may be exploited via combinatorial chemistry and high-throughput screening. High-throughput assays can be run rapidly and inexpensively and, due to their scale, allow access to the structural variety granted by combinatorial chemistry. In addition, potential lead compounds can be directly counterscreened on the same target cloned from human or beneficial insect sources to exclude broad spectrum toxins. The essential functions of target genes in insects and nematodes may be tested directly using powerful genetic methods, eliminating the costly uncertainty of whether or not a specific gene or biochemical activity might be a pesticide target. The phenotypic consequence of genetically modulating target gene activity serves as a surrogate for chemical inhibition or activation of a protein target. Thus, genes that kill the organism when over-expressed or knocked out represent first-stage validated targets. To identify compounds that have the same effect on the organism, high-throughput screening assays are established to test compounds for their ability to interfere in vitro with the normal activity of the target. Biological definition of targets provides the opportunity to optimize chemistry around validated targets. Ion channels are validated targets of insecticide action. A significant portion of commercial insecticides are targeted towards GABA-gated chloride channels and voltage-gated sodium channels. Potassium channels, as a diverse group, have yet to be fully exploited as targets for insecticidal agents. Potassium ion channels are involved in numerous cellular functions in a variety of cell types, and recent advances in genomics and physiology have identified several potassium channels that are involved in human diseases (Doyle et al., Trends. Genet. (1998) 14: 92-98). In particular, members of the TWIK family show strong expression in the brain and the heart, followed by expression in the kidney and the muscle (Lesage et al., supra), and thus, could be implicated in epilepsy, cardiac pathologies (arrhythmias), vascular defects, neurodegenerative disorders, endocrinopathies, hormone secretion and muscular defects, and genetic diseases. The growing body of information regarding the modular subunits and the high-resolution structural of these channels features (Doyle et al., Science (1998) 280: 69-77) provide critical information for validation of potassium channels as drug targets. The identification of novel TWIK orthologues in model organisms such as Drosophila melanogaster and other insect species would provide tools for genetic and molecular study and validation of these molecules as potential pesticide or pharmaceutical targets. SUMMARY OF THE INVENTION The present invention relates to the identification and characterization of novel TWIK channels in Drosophila melanogaster and Leptinotarsa decemlineata. Isolated nucleic acid molecules are provided that encode TWIK channel proteins or novel fragments or derivatives thereof. Vectors and host cells comprising the TWIK channel nucleic acid molecules are also described, as well as metazoan invertebrate organisms (e. g. insects, coelomates and pseudocoelomates) that are genetically modified to express or mis-express a TWIK channel protein. An important utility of the novel TWIK channel nucleic acids and proteins of the present invention is that they can be used in screening assays to identify candidate compounds which are potential pesticidal agents or therapeutics that interact with TWIK channel proteins. Such assays typically comprise contacting a TWIK channel protein or fragment with one or more candidate molecules, and detecting any interaction between the candidate compound and the TWIK channel protein. The assays may comprise administering the candidate molecules to cultured host cells that have been genetically engineered to express the TWIK channel proteins, or alternatively, administering the candidate compound to a metazoan invertebrate organism that has been genetically engineered to express a TWIK channel protein. The genetically engineered metazoan invertebrate animals of the invention can also be used in methods for studying TWIK channel activity. These methods typically involve detecting the phenotype caused by the expression or mis-expression of the TWIK channel protein. The methods may additionally comprise observing a second animal that has the same genetic modification as the first but additionally comprises a mutation in a gene of interest. Differences, if any, between the phenotypes of the two animals identifies the gene of interest as capable of modifying the function of the gene encoding the TWIK channel protein. BRIEF DESCRIPTION OF FIGURES Fig. 1 depicts a representative TWIK channel. DETAILED DESCRIPTION OF THE INVENTION The use of invertebrate model organism genetics and related technologies can greatly facilitate the elucidation of biological pathways (Scangos, Nat. Biotechnol. (1997) 15: 12201221; Margolis and Duyk, supra). Of particular use is the insect model organism, Drosophila melanogaster (hereinafter referred to generally as"Drosophila"). An extensive search for TWIK channel nucleic acids and their encoded proteins in Drosophila and Leptinotarsa decemlineata (Colorado Potato Beetle, hereinafter referred to as"Leptinotarsa") was conducted in an attempt to identify new and useful tools for probing the function and regulation of the TWIK channel genes, and for use as targets in pesticide and drug discovery. Novel TWIK channel nucleic acids and their encoded proteins are identified herein. These newly identified TWIK channel nucleic acids can be used for the generation of mutant phenotypes in animal models or in living cells that can be used to study the ion channels, their regulation, and their use as pesticide or drug targets. The use of invertebrate model organisms such as Drosophila for analyzing the expression and mis-expression of TWIK channel proteins has great utility toward the identification of drug targets or mechanism of drug action, due to the ability to rapidly carry out large-scale, systematic genetic screens as well as the ability to screen small molecule libraries directly on whole organisms. Thus, the invention provides a superior approach for identifying other components involved in the synthesis, activity, and regulation of TWIK channel proteins. Systematic genetic analysis of TWIK channels using invertebrate model organisms can lead to the identification and validation of pesticide targets directed to components of the TWIK channel pathway. Additionally, these invertebrate model organisms can be used for the screening and identification of new drug targets, therapeutic agents, diagnostics and prognostics useful in the treatment of disorders associated with ion channels. The details of the conditions used for the identification and/or isolation of each novel TWIK channel nucleic acid and protein are described in the Examples section below. Various non-limiting embodiments of the invention, applications and uses of these novel TWIK channel genes and proteins are discussed in the following sections. The entire contents of all references, including patent applications, cited herein are incorporated by reference in their entireties for all purposes. Additionally, the citation of a reference in the preceding background section is not an admission of prior art against the claims appended hereto. TWIK CHANNEL NUCLEIC ACIDS The invention relates generally to TWIK channel nucleic acid, and more particularly TWIK channel nucleic acid sequences of Drosophila and Leptinotarsa, and methods of using these sequences. As described in the Examples below, the present invention provides nucleic acid sequences (SEQ ID NO: 1,3,5,7,9, and 11) that were isolated from Drosophila and encode TWIK channel homologues referred to herein as TWIK2, TWIK3, TWIK4, TWIK5, TWIK6, and TWIK7, respectively. The invention also provides a nucleic acid sequence (SEQ ID NO: 13) isolated from Leptinotarsa that encodes a TWIK channel referred to herein as "cpbTWIKI". In addition to the fragments and derivatives of SEQ ID NOs 1,3,5,7,9,11, and 13 as described in detail below, the invention includes the reverse complements thereof. Also, the subject nucleic acid sequences, derivatives and fragments thereof may be RNA molecules comprising the nucleotide sequence of any one of SEQ ID NOs 1,3,5,7,9,11, and 13 (or derivative or fragment thereof) wherein the base U (uracil) is substituted for the base T (thymine). The DNA and RNA sequences of the invention can be single-or double-stranded. Thus, the term"isolated nucleic acid sequence", as used herein, includes the reverse complement, RNA equivalent, DNA or RNA single-or double-stranded sequences, and DNA/RNA hybrids of the sequence being described, unless otherwise indicated. Fragments of these TWIK channel nucleic acid sequences can be used for a variety of purposes, for example, as nucleic acid hybridization probes and replication/amplification primers. Certain"antisense"fragments, i. e. that are reverse complements of portions of the coding sequences set forth in any one of SEQ ID NOs: 1,3,5,7,9,11, and 13, have utility in inhibiting the function of TWIK channel genes and proteins. The fragments are of length sufficient to specifically hybridize with the corresponding SEQ ID NO 1,3,5,7,9,11, or 13. In particular, the invention provides fragments of at least 12, preferably at least 24, more preferably at least 36, and more preferably at least 96 contiguous nucleotides of any one of SEQ ID NOs: 1, 3,5,7,9,11, and 13. When the fragments are flanked by other nucleic acid sequences, the total length of the combined nucleic acid sequence is usually less than 15 kb, preferably less than 10 kb or less than 5kb, more preferably less than 2 kb, and in some embodiments, preferably less than 500 bases. Preferred fragments of TWIK2 (SEQ ID NO: 1) include those having at least 1791 contiguous nucleotides of SEQ ID NO: 1, and more preferably at least 1796 nucleotides. Another preferred fragment comprises or consists of a sequence that encodes one of the P domains which are located at approximately nucleotides 1902-1971 and 2433-2499 of SEQ ID NO: 1. Other possible fragments include those that encode TM domains which are located at approximately nucleotides 1668-1716,2028-2076,2412-2460, and 2568-2616 of SEQ ID NO: 1. Other preferred fragments comprise any one of the following contiguous sequences of SEQ ID NO: 1: nucleotides 1-1796,1791-1803,1786-1954,1949-1961, and 1944-2988. Preferred fragments of TWIK3 (SEQ ID NO: 3) include those having at least 1403 contiguous nucleotides of SEQ ID NO: 3, and more preferably at least 1408 nucleotides. In another embodiment of the invention, a fragment containing approximately nucleotides 405-477, or 1938-2007 of SEQ ID NO: 3, which encode the P domains. In a further embodiment of the invention, a fragment containing approximately any of nucleotides 102-150,507-555,19021950, or 2076-2124 of SEQ ID NO: 3, which encode the TM domains. Other preferred fragments comprise any one of the following contiguous sequences of SEQ ID N0: 3: nucleotides 1-216,207-457,448-588,579-1992, and 1983-2193. Preferred fragments of TWIK4 (SEQ ID NO: 5) include those having at least 350 contiguous nucleotides of SEQ ID NO: 5, and more preferably at least 355 nucleotides. In another embodiment of the invention, a fragment containing approximately nucleotides 381-453, or 933-1002 of SEQ ID N0: 5, which encode the P domains. In a further embodiment of the invention, a fragment containing approximately any of nucleotides 102-150,477-525,861-909, or 1065-1113 of SEQ ID NO: 5, which encode the TM domains. Other preferred fragments comprise any one of the following contiguous sequences of SEQ ID NO: 5: nucleotides 1-311, 306-318,302-661,656-668,652-896,891-903,887-1018,1013-1025,1009-1122,1117-1129, and 1112-1188. Preferred fragments of TWIK5 (SEQ ID NO: 7) include those having at least 660 contiguous nucleotides of SEQ ID NO: 7, and more preferably at least 665 nucleotides. In another embodiment of the invention, a fragment containing approximately nucleotides 573-642, or 3228-3297 of SEQ ID N0: 7, which encode the P domains. In a further embodiment of the invention, a fragment containing approximately any of nucleotides 222-282,663-723,31473210, or 3339-3411 of SEQ ID N0: 7, which encode the TM domains. Other preferred fragments comprise any one of the following contiguous sequences of SEQ ID N0: 7: nucleotides 1-372,368-629,620-898,889-1161,1152-1354,1345-1425,1416-1532,1523-2146, 2137-2269,2260-2325,2316-2806,2797-3462. Preferred fragments of TWIK6 (SEQ ID NO: 9) include those that comprise or consist of approximately nucleotides 45-105, encoding a P domain, and approximately nucleotides 124191, encoding a TM domain. Preferred fragments of TWIK7 (SEQ ID NO: 11) include those having at least 440 contiguous nucleotides of SEQ ID NO: 11, and more preferably at least 445 nucleotides. In another embodiment of the invention, a fragment containing approximately nucleotides 234-303, or 552-621 of SEQ ID NO: 11, which encode the P domains. In a further embodiment of the invention, a fragment containing approximately any of nucleotides 27-75,327-375,483-531, or 672-720 of SEQ ID NO: 11, which encode the TM domains. Other preferred fragments comprise any one of the following contiguous sequences of SEQ ID NO: 11: nucleotides 1-131, 126-138,122-288,283-295,279-412,407-419,403-606,601-613,597-792,787-799,783-954, 949-961,945-987,982-994, and 978-1231. Preferred fragments of cpbTWIKI (SEQ ID NO: 13) include those containing approximately residues 561-633, or 891-963 of SEQ ID NO: 13, which encode the P domains. In another preferred embodiment of the invention, a fragment containing approximately any of nucleotides 324-366,654-714,798-879, or 1008-1074 of SEQ NË: 13, which encode the TM domains. The subject nucleic acid sequences may consist solely of any one of SEQ ID NOs: 1,3,5, 7,9,11, or 13, or fragments thereof. Alternatively, the subject nucleic acid sequences and fragments thereof may be joined to other components such as labels, peptides, agents that facilitate transport across cell membranes, hybridization-triggered cleavage agents or intercalating agents. The subject nucleic acid sequences and fragments thereof may also be joined to other nucleic acid sequences (i. e. they may comprise part of larger sequences) and are of synthetic/non-natural sequences and/or are isolated and/or are purified, i. e. unaccompanied by at least some of the material with which it is associated in its natural state. Preferably, the nucleic acids constitute at least about 0.5%, and more preferably at least about 5% by weight of the total nucleic acid present in a given fraction, and are preferably recombinant, meaning that they comprise a non-natural sequence or a natural sequence joined to nucleotide (s) other than that which it is joined to on a natural chromosome. The invention also provides derivative nucleic acid sequences which hybridize to the nucleic acid sequence of any one of SEQ ID NOs: l, 3,5,7,9,11, and 13 under stringency conditions such that each hybridizing derivative nucleic acid is related to the subject nucleic acid by a certain degree of sequence identity. The temperature and salt concentrations at which hybridizations are performed have a direct effect on the results that are obtained. With "stringent"or"high stringency"conditions, a denaturing agent, such as formamide, is used during hybridization. The formamide is typically used at 25% to 50% (v/v) in a buffered diluent comprising 1X to 6X SSC (1X SSC is 150 mM NaCl and 15mM sodium citrate; SSPE may be substituted for SSC, 1X SSPE is 150mM NaCl, 10 mM Na H2PO4, and 1.25 mM EDTA, pH7.4). The hybridization temperature is typically about 42 C. High stringency conditions also employ a wash buffer with low ionic strength, such as 0.1X to about 0.5X SSC, at relatively high temperature, typically greater than about 55 C up to about 70 C. Moderately stringent conditions typically use 0% to 25% formamide in 1X to 6X SSC, and use reduced hybridization temperatures, usually in the range of about 27 C to about 40 C. The wash buffer can have increased ionic strength, e. g. about 0.6X to about 2X SSC, and is used at reduced temperatures, usually from about 45 C to about 55 C. With"non-stringent"or"low stringency"hybridization conditions, the hybridization buffer is the same as that used for moderately stringent or high stringency, but does not contain a denaturing agent. A reduced hybridization temperature is used, typically in the range of about 25 C to about 30 C. The wash buffer has increased ionic strength, usually around 2X to about 6X SSC, and the wash temperature is in the range of about 35 C to about 47 C. Procedures for nucleic acid hybridizations are well-known in the art (Ausubel et al., Current Protocols in Molecular Biology (1995) Wiley Interscience Publishers; Sambrook et a/., Molecular Cloning: A Laboratory Manual (1989) Cold Spring Harbor Press, New York; Shilo and Weinberg, PNAS (1981) 78: 6789-6792). In a specific embodiment of the invention, nucleic acids are provided that are capable of hybridizing to any one of SEQ ID NOs: 1,3,5,7,9,11, and 13, or the above-specified fragments thereof, under any one of the hybridization conditions listed in Table 1. Hybridization conditions 8-10, as listed in Table 1, are generally considered"high stringency"conditions; conditions 4-7 are generally considered"moderately stringent", and conditions 1-3 are considered"non-stringent". TABLE I EMI9.1 <tb> Condition <SEP> &num; <SEP> Hybridization <SEP> Hybridization <SEP> Wash <SEP> Buffer <SEP> Wash <tb> <SEP> Buffer <SEP> Temperature <SEP> Temperature <tb> <SEP> 6X <SEP> SSC/0% <tb> <SEP> 1 <SEP> forrnamide <SEP> 25 <SEP> C <SEP> 4X <SEP> SSC <SEP> 35 <SEP> C <tb> <SEP> 6X <SEP> SSC/0% <tb> <SEP> 2 <SEP> formamide <SEP> 25 <SEP> C <SEP> 4X <SEP> SSC <SEP> 40 <SEP> C <tb> <SEP> 6X <SEP> SSC/0% <tb> <SEP> 3 <SEP> formamide <SEP> 27 <SEP> C <SEP> 4X <SEP> SSC <SEP> 47 <SEP> C <tb> <SEP> /0%6XSSC <SEP> <tb> <SEP> 4 <SEP> formamide <SEP> 34 <SEP> C <SEP> 2X <SEP> SSC <SEP> 450 <SEP> C <tb> <SEP> /0%6XSSC <SEP> <tb> <SEP> 5 <SEP> forrnamide <SEP> 40 <SEP> C <SEP> 0. <SEP> 8X <SEP> SSC <SEP> 45 <SEP> C <tb> <SEP> 3X <SEP> SSC/0% <tb> <SEP> 6 <SEP> formamide <SEP> 40 <SEP> C <SEP> 0.6X <SEP> SSC <SEP> 50 <SEP> C <tb> <SEP> 1X <SEP> SSC/0% <tb> <SEP> 7 <SEP> formamide <SEP> 40 <SEP> C <SEP> 0.6X <SEP> SSC <SEP> 55 <SEP> C <tb> <SEP> 6X <SEP> SSC/25% <tb> <SEP> 8 <SEP> formamide <SEP> 42 <SEP> C <SEP> 0. <SEP> 5X <SEP> SSC <SEP> 60 <SEP> C <tb> <SEP> 2X <SEP> SSC/25% <tb> <SEP> 9 <SEP> t <SEP> rmamide <SEP> 420 <SEP> C <SEP> 0.4X <SEP> SSC <SEP> 65 <SEP> C <tb> <SEP> 1X <SEP> SSC/25% <tb> <SEP> 10 <SEP> formamide <SEP> 42 <SEP> C <SEP> 0. <SEP> 3X <SEP> SSC <SEP> 70 <SEP> C <tb> Condition &num;1 shown in Table 1 is designed to isolate nucleic acids having at least about 50% sequence identity with the target nucleic acid (with % identity calculated as described below). With each subsequent condition, the stringency is such that the isolated nucleic acid has a sequence identity of at least 5% greater than what would be isolated by using the next lower condition number. Thus, for example, condition &num;2 is designed to isolate nucleic acids having at least about 55% sequence identity with the target nucleic acid, and conditions &num;9 and &num;10 are designed to isolate nucleic acids having at least about 90% and 95% sequence identity, respectively, to the target nucleic acid. Preferably, each hybridizing derivative nucleic acid has a length that is at least 30% of the length of the subject nucleic acid sequence described herein to which it hybridizes. More preferably, the hybridizing nucleic acid has a length that is at least 50%, still more preferably at least 70%, and most preferably at least 90% of the length of the subject nucleic acid sequence to which it hybridizes. As used herein,"percent (%) nucleic acid sequence identity"with respect to a subject sequence, or a specified portion of a subject sequence, is defined as the percentage of nucleotides in the candidate derivative nucleic acid sequence identical with the nucleotides in the subject sequence (or specified portion thereof), after aligning the sequences and introducing gaps, if necessary to achieve the maximum percent sequence identity, as generated by the program WU-BLAST-2.0al9 (Altschul et al., J. Mol. Biol. (1997) 215: 403-410; http://blast. wustl. edu/blast/README. html ; hereinafter referred to generally as"BLAST") with all the search parameters set to default values. The HSP S and HSP S2 parameters are dynamic values and are established by the program itself depending upon the composition of the particular sequence and composition of the particular database against which the sequence of interest is being searched. A percent (%) nucleic acid sequence identity value is determined by the number of matching identical nucleotides divided by the sequence length for which the percent identity is being reported. Preferably, derivative nucleic acid sequences of the present invention have at least 70%, preferably at least 80%, more preferably at least 85%, still more preferably at least 90%, and most preferably at least 95% sequence identity with any one of SEQ ID NOs: 1,3,5,7, 9,11, and 13. In some preferred embodiments, the derivative nucleic acid encodes a polypeptide comprising a TWIK channel amino acid sequence of any one of SEQ ID NOs: 2,4, 6,8,10,12, and 14, or a fragment thereof. If a fragment of a TWIK channel amino acid sequence is encoded, preferably it is a functionally active fragment (e. g. a P domain, TM domain, antigenic determinant, etc.). Various domains, signals, and otherfunctional subunits of TWIK channels can be predicted using the PSORT programs (Nakai and Horton, Trends Biochem. Sci. (1999) 24: 34-36; http://psort. nibb. ac. jp: 8800/) and/or PFAM (Bateman et al., Nucleic Acids Res. (1999) 27: 260-262; http://pfam. wustl. edu). In one embodiment, the TWIK channel protein fragments encoded by the TWIK channel nucleic acids, or derivative nucleic acids, preferably comprise at least 10 contiguous amino acids, more preferably at least 12 contiguous amino acids, still more preferably at least 15 contiguous amino acids, and most preferably at least 20 contiguous amino acids of any one of SEQ ID NOs: 2,4,6,8,10, and 14. Alternatively, the encoded TWIK channel protein fragments comprise at least 20 contiguous amino acids, more preferably at least 25, and most preferably at least 30 contiguous amino acids that share 100% sequence similarity with a contiguous stretch of amino acids of the same length of any one of SEQ ID NOs: 2,4,6,8,10 and 14. I fragments comprise at least 35 contiguous amino acids, more preferably at least 40, and most preferably at least 45 contiguous amino acids that share 100% sequence similarity with a contiguous stretch of amino acids of the same length of any one of SEQ ID NOs: 2,4,6,8,10, 12, and 14. More specific embodiments of preferred TWIK channel protein fragments and derivatives are discussed further below in connection with specific TWIK channel proteins. A derivative of the subject nucleic acid sequence, or fragment thereof, may comprise 100% sequence identity with the subject nucleic acid sequence, but be a derivative thereof in the sense that it has one or more modifications at the base or sugar moiety, or phosphate backbone. Examples of modifications are well known in the art (Bailey, Ullmann's Encyclopedia of Industrial Chemistry (1998), 6th ed. Wiley and Sons). Such derivatives may be used to provide modified stability or any other desired property. Another type of derivative of the subject nucleic acid sequences includes corresponding humanized sequences. A humanized nucleic acid sequence is one in which one or more codons has been substituted with a codon that is more commonly used in human genes. Preferably, a sufficient number of codons have been substituted such that a higher level expression is achieved in mammalian cells than what would otherwise be achieved without the substitutions. The following list shows, for each amino acid, the calculated codon frequency (number in parentheses) in humans genes for 1000 codons (Wada et al., Nucleic Acids Research (1990) 18 (Suppl.) : 2367-2411): ARG: CGA (5.4), CGC (11.3), CGG (10.4), CGU (4.7), AGA (9.9), AGG (11.1) LEU: CUA (6.2), CUC (19.9), CUG (42.5), CW (10.7), WA (5.3), UUG (11.0) SER: UCA (9.3), UCC (17.7), UCG (4.2), UCU (13.2), AGC (18.7), AGU (9.4) THR: ACA (14.4), ACC (23.0), ACG (6.7), ACU (12.7) PRO: CCA (14.6), CCC (20.0), CCG (6.6), CCU (15.5) ALA: GCA (14.0), GCC (29.1), GCG (7.2), GCU (19.6) GLY: GGA (17.1), GGC (25.4), GGG (17.3), GGU (11.2) VAL: GUA (5.9), GUC (16.3), GUG (30.9), GW (10.4) LYS: AAA (22.2), AAG (34.9) ASN: AAC (22.6), AAU (16.6) GLN: CAA (11.1), CAG (33.6) HIS: CAC (14.2), CAU (9.3) GLU: GAA (26.8), GAG (41.4) ASP: GAC (29.0), GAU (21.7) TYR: UAC (18.8), UAU (12.5) CYS: UGC (14.5), UGU (9.9) PHE: UUU (22.6), UUC (15.8) ILE: AUA (5.8), AUC (24.3), AUU (14.9) MET: AUG (22.3) TRP: UGG (13.8) TER: UAA (0.7), AUG (0.5), UGA (1.2) Thus, a TWIK channel nucleic acid sequence in which the glutamic acid codon, GAA has been replaced with the codon GAG, which is more commonly used in human genes, is an example of a humanized TWIK channel nucleic acid sequence. A detailed discussion of the humanization of nucleic acid sequences is provided in U. S. Pat. No. 5,874,304 to Zolotukhin et al. In various embodiments, the nucleic acids of the invention are less than 15 kb, 10 kb, 5 kb, or 2 kb, or less than 500 bases. In a specific embodiment, the invention provides an isolated nucleic acid molecule of less than about 15 kb in size comprising a nucleic acid sequence selected from the group consisting of : (a) a nucleic acid sequence that encodes a polypeptide comprising at least x contiguous amino acids of any one of SEQ ID NOs: 2,4,6,8,10,12, and 14, wherein for each respective SEQ ID NO, x is the number of amino acids listed in the column entitled"100% identity length x"in Table 4; (b) a nucleic acid sequence that encodes a polypeptide comprising at least y amino acids that share 100% sequence identity or similarity withy amino acids of any one of SEQ ID NOs: 2, 4,6,8,10,12, and 14, wherein for each respective SEQ ID NO, y is the number of amino acids listed in the column entitled"100% identity or similarity lengthy"in Table 4; and (c) the complement of the nucleic acid sequence of (a) or (b). ISOLATION, PRODUCTION, AND EXPRESSION OF TWIK CHANNEL NUCLEIC ACIDS Nucleic acid encoding the amino acid sequence of any one of SEQ ID NOs: 2,4,6,8,10, 12, and 14, may be obtained from an appropriate cDNA library prepared from any eukaryotic species that encodes TWIK channel proteins such as vertebrates, preferably mammalian (e. g. primate, porcine, bovine, feline, equine, and canine species, etc.) and invertebrates, such as arthropods, particularly insects species (preferably Drosophila and Leptotarsa), acarids, crustacea, molluscs, coelomates and pseudocoelomates. An expression library can be constructed using known methods. For example, mRNA can be isolated to make cDNA which is ligated into a suitable expression vector for expression in a host cell into which it is introduced. Various screening assays can then be used to select for the gene or gene product (e. g. oligonucleotides of at least about 20 to 80 bases designed to identify the gene of interest, or labeled antibodies that specifically bind to the gene product). The gene and/or gene product can then be recovered from the host cell using known techniques. Polymerase chain reaction (PCR) can also be used to isolate nucleic acids of the TWIK channel where oligonucleotide primers representing fragmentary sequences of interest amplify RNA or DNA sequences from a source such as a genomic or cDNA library (as described by Sambrook et al., supra). Additionally, degenerate primers for amplifying homologues from any species of interest may be used. Once a PCR product of appropriate size and sequence is obtained, it may be cloned and sequenced by standard techniques, and utilized as a probe to isolate a complete cDNA or genomic clone. Fragmentary sequences of SEQ ID NOs 1,3,5,7,9,11, and 13 may be synthesized by known methods. For example, oligonucleotides may be synthesized using an automated DNA synthesizer available from commercial suppliers (e. g. Biosearch, Novato, CA; Perkin-Elmer Applied Biosystems, Foster City, CA). Antisense RNA sequences can be produced intracellularly by transcription from an exogenous sequence, e. g. from vectors that contain antisense TWIK channel nucleic acid sequences. Newly generated sequences may be identified and isolated using standard methods. An isolated TWIK channel nucleic acid sequence can be inserted into any appropriate cloning vector, for example bacteriophages such as lambda derivatives, or plasmids such as PBR322, pUC plasmid derivatives and the Bluescript vector (Stratagene, San Diego, CA). Recombinant molecules can be introduced into host cells via transformation, transfection, infection, electroporation, etc. The transformed cells can be cultured to generate large quantities of the TWIK channel nucleic acid. Suitable methods for isolating and producing the subject nucleic acid sequences are well-known in the art (Sambrook et al., supra; DNA Cloning: A Practical Approach, Vol. 1,2,3,4, (1995) Glover, ed., MRL Press, Ltd., Oxford, U. K.). The nucleotide sequence encoding a TWIK channel protein or fragment or derivative thereof, can be inserted into any appropriate expression vector for the transcription and translation of the inserted protein-coding sequence. Alternatively, the necessary transcriptional and translational signals can be supplied by the native TWIK channel gene and/or its flanking regions. A variety of host-vector systems may be utilized to express the protein-coding sequence such as mammalian cell systems infected with virus (e. g. vaccina virus, adenovirus, etc.); insect cell systems infected with virus (e. g. baculovirus); microorganisms such as yeast containing yeast vectors, or bacteria transformed with bacteriophage, DNA, plasmid DNA, or cosmid DNA. Expression of a TWIK channel protein may be controlled by a suitable promoter/enhancer element. In addition, a host cell strain may be selected which modulates the expression of the inserted sequences, or modifies and processes the gene product in the specific fashion desired. In a specific embodiment, a vector is used that comprises a promoter operably linked to a TWIK channel gene nucleic acid, one or more origins of replication, and, one or more selectable markers (e. g. thymidine kinase activity, resistance to antibiotics, etc.) so that expression of the gene product can be detected. Alternatively, recombinant expression vectors can be identified by assaying for the expression of the TWIK channel gene product based on the physical or functional properties of the TWIK channel protein in in vitro assay systems (e. g. immunoassays). In a specific embodiments, the TWIK channel protein, fragment, or derivative may be expressed as a fusion, or chimeric protein product (i. e. it is joined via a peptide bond to a heterologous protein sequence of a different protein). Such a chimeric product can be made by ligating the appropriate nucleic acid sequences encoding the desired amino acid sequences to each other in the proper coding frame (using methods known in the art) and expressing the chimeric product. Alternatively, such a chimeric product may be made by protein synthetic techniques, e. g. by use of a peptide synthesizer. Once a recombinant which expresses the TWIK channel gene sequence is identified, the gene product can be isolated using standard methods (e. g. ion exchange, affinity, and sizing column chromatography; centrifugation; differential solubility). The amino acid sequence of the protein can be deduced from the nucleotide sequence of the chimeric gene contained in the recombinant. As a result, the protein can be synthesized by standard chemical methods known in the art (Hunkapiller et al., Nature (1984) 310: 105-111). Alternatively, native TWIK channel proteins can be purified from natural sources, by standard methods (e. g. immunoaffinity purification). TWIK CHANNEL PROTEINS The invention provides TWIK channel proteins that comprise or consist of an amino acid sequence of any one of SEQ ID NOs: 2,4,6,8,10,12, and 14 or fragments or derivatives thereof. Compositions comprising these proteins may consist essentially of the TWIK channel proteins. Alternatively, the TWIK channel proteins may be a component of a composition that comprises other components (e. g. a diluent such as saline, a pharmaceutically acceptable carrier or excipient, a culture medium, carriers used in pesticide formulations, etc.). Typically, a derivative of a TWIK channel protein will share a certain degree of sequence identity or sequence similarity with any one of SEQ ID NOs 2,4,6,8,10,12, and 14, or a fragment thereof. As used herein,"percent (%) amino acid sequence identity"with respect to a subject sequence, or a specified portion of a subject sequence, is defined as the percentage of amino acids in the candidate derivative amino acid sequence identical with the amino acid in the subject sequence (or specified portion thereof), after aligning the sequences and introducing gaps, if necessary to achieve the maximum percent sequence identity, as generated by BLAST (Altschul et al., supra) using the same parameters discussed above for derivative nucleic acid sequences. A % amino acid sequence identity value is determined by the number of matching identical amino acids divided by the sequence length for which the percent identity is being reported. Preferably, derivative amino acid sequences of the present invention have at least 80%, preferably at least 85%, more preferably at least 90%, and most preferably at least 95% sequence identity with any contiguous stretch of at least 20 amino acids, preferably at least 25 amino acids, more preferably at least 30 amino acids, and in some cases, the entire length of any one of SEQ ID NOs 2,4,6,8,10,12, and 14. In some embodiments, the contiguous stretch of amino acids encodes a P or TM domain of the TWIK channel polypeptide."Percent (%) amino acid sequence similarity"is determined by doing the same calculation as for determining % amino acid sequence identity described above, but including conservative amino acid substitutions in additional to identical amino acids in the computation. A conservative amino acid substitution is one in which an amino acid is substituted for another amino acid having similar properties such that the folding or activity of the protein is not significantly affected. Aromatic amino acids that can be substituted for each other are phenylalanine, tryptophan, and tyrosine; interchangeable hydrophobic amino acids are leucine, isoleucine and valine; interchangeable polar amino acids are glutamine and asparagine; interchangeable basic amino acids arginine, lysine and histidine; interchangeable acidic amino acids aspartic acid and glutamic acid; and interchangeable small amino acids alanine, serine, threonine, methionine, and glycine. A preferred derivative of TWIK2 consists of or comprises an amino acid sequence that has at least 55%, preferably at least 60%, and more preferably, at least 65% sequence identity with any of amino acid residues 634-657, or 811-833 of SEQ ID NO: 2 (i. e. the P domains), or any of amino acid residues 556-572,676-692,804-820, or 856-872 of SEQ ID NO: 2 (i. e. the TM domains). Other preferred amino acid derivatives of TWIK2 consist of or comprise an amino acid sequence that shares at least 75% similarity, preferably at least 80% similarity, and more preferably, at least 85% similarity with any of amino acid residues 634-657,811-833,556572,676-692,804-820, or 856-872 of SEQ ID NO: 2. In another embodiment, a preferred derivative of TWIK2 consists of or comprises an amino acid sequence that shares 100% sequence similarity with any of at least 15, preferably at least 16, more preferably at least 17, and most preferably at least 18 contiguous amino acids of SEQ ID NO: 2. A preferred derivative of TWIK3 consists of or comprises an amino acid sequence that has at least 55%, preferably at least 60%, and more preferably, at least 65% sequence identity with any of amino acid residues 135-159, or 646-669 of SEQ ID NO: 4 (i. e. the P domains), or any of amino acid residues 34-50,169-185,634-650, or 692-708 of SEQ ID NO: 4 (i. e. the TM domains). Other preferred amino derivatives of TWIK3 consist of or comprise an amino acid sequence that shares at least 75% similarity, preferably at least 80% similarity, and more preferably, at least 85% similarity with any of amino acid residues of 135-159,646-669,34-50, 169-185,634-650, or 692-708 of SEQ ID NO: 4. In another embodiment, a preferred derivative of TWIK3 consists of or comprises an amino acid sequence that shares 100% sequence similarity with any of at least 17, preferably at least 18, more preferably at least 19, and most preferably at least 20 contiguous amino acids of SEQ ID NO: 4. A preferred derivative of TWIK4 consists of or comprises an amino acid sequence that has at least 55%, preferably at least 60%, and more preferably, at least 65% sequence identity with any of amino acid residues 127-151, or 311-334 of SEQ ID NO: 6 (i. e. the P domains), or any of amino acid residues 34-50,159-175,287-303, or 355-371 of SEQ ID NO: 6 (i. e. the TM domains). Other preferred amino derivatives of TWIK4 consist of or comprise an amino acid sequence that shares at least 75% similarity, preferably at least 80% similarity, and more preferably, at least 85% similarity with any of amino acid residues 127-151,311-334,34-50, 159-175,287-303, or 355-371 of SEQ ID N0: 6. In another embodiment, a preferred derivative of TWIK4 consists of or comprises an amino acid sequence that shares 100% sequence similarity with any of at least 16, preferably at least 17, more preferably at least 18, and most preferably at least 19 contiguous amino acids of SEQID NO: 6. A preferred derivative of TWIK5 consists of or comprises an amino acid sequence that has at least 55%, preferably at least 60%, and more preferably, at least 65% sequence identity with any of amino acid residues 191-214, or1076-1099 of SEQ ID NO: 8 (i. e. the P domains), or any of amino acid residues 74-94,221-241,1049-1070, or 1113-1137 of SEQ ID NO: 8 (i. e. the TM domains). Other preferred amino derivatives of TWIK5 consist of or comprise an amino acid sequence that shares at least 75% similarity, preferably at least 80% similarity, and more preferably, at least 85% similarity with any of amino acid residues 191-214,1076-1099,74-94, 221-241,1049-1070, or 1113-1137 of SEQ ED NO: 8. In another embodiment, a preferred derivative of TWIK5 consists of or comprises an amino acid sequence that shares 100% sequence similarity with any of at least 18, preferably at least 19, more preferably at least 20, and most preferably at least 21 contiguous amino acids of SEQ ID NO: 8. A preferred derivative of TWIK6 consists of or comprises an amino acid sequence that has at least 55%, preferably at least 60%, and more preferably, at least 65% sequence identity with amino acid residues 15-35 of SEQID NO: 10 (i. e. a P domains), or any of amino acid residues 45-105 of SEQ ID NO: 10 (i. e. a TM domain). Other preferred amino derivatives of TWIK6 consist of or comprise an amino acid sequence that shares at least 75% similarity, preferably at least 80% similarity, and more preferably, at least 85% similarity with any of amino acid residues 15-35 or 45-105 of SEQ ID NO: 10. In another embodiment, a preferred derivative of TWIK6 consists of or comprises an amino acid sequence that shares 100% sequence similarity with any of at least 15, preferably at least 16, more preferably at least 17, and most preferably at least 18 contiguous amino acids of SEQ IID NO: 10. A preferred derivative of TWIK7 consists of or comprises an amino acid sequence that has at least 55%, preferably at least 60%, and more preferably, at least 65% sequence identity with any of amino acid residues 78-101, or 184-207 of SEQID NO: 12 (i. e. the P domains), or any of amino acid residues 9-25,109-125,161-177, or 224-240 of SEQ ID NO: 12 (i. e. the TM domains). Other preferred amino derivatives of TWIK7 consist of or comprise an amino acid sequence that shares at least 75% similarity, preferably at least 80% similarity, and more preferably, at least 85% similarity with any of amino acid residues 78-101,184-207,9-25,109125,161-177, or 224-240 of SEQ ID N0: 12. In another embodiment, a preferred derivative of TWIK7 consists of or comprises an amino acid sequence that shares 100% sequence similarity with any of at least 31, preferably at least 32, more preferably at least 33, and most preferably at least 34 contiguous amino acids of SEQ ID NO: 12. A preferred derivative of cpbTWIKI consists of or comprises an amino acid sequence that has at least 55%, preferably at least 60%, and more preferably, at least 65% sequence identity with any of amino acid residues 125-149, or 235-259 of SEQ ID NO: 14 (i. e. the P domains), or any of amino acid residues 46-60,156-176,204-231, or 274-296 of SEQ ID NO: 14 (i. e. the TM domains). Other preferred amino derivatives of cpbTWIKI consist of or comprise an amino acid sequence that shares at least 75% similarity, preferably at least 80% similarity, and more preferably, at least 85% similarity with any of amino acid residues 125-149,235-259, 46-60,156-176,204-231, or 274-296 of SEQID NO: 14. In another embodiment, a preferred derivative of cpbTWIKI consists of or comprises an amino acid sequence that shares 100% sequence similarity with any of at least 20, preferably at least 21, more preferably at least 22, and most preferably at least 23 contiguous amino acids of SEQ ID NO: 14. The invention also provides proteins having amino acid sequences that consist of or comprise a fragment of any one of SEQ ID NOs 2,4,6,8,10,12, and 14. The fragments usually have at least 24, preferably at least 26, more preferably at least 30, and most preferably at least 45 contiguous amino acids of any one of SEQ ID NOs 2,4,6,8,10,12, and 14. In certain embodiments, the following fragments are preferred: at least 8, preferably at least 9, more preferably at least 10, and most preferably at least 11 contiguous amino acids of any of SEQ ID NO: 2, SEQ ID NO: 6, SEQ ID NO: 8, and SEQ ID NO: 14; at least 7, preferably at least 8, more preferably at least 9, and most preferably at least 10 contiguous amino acids of SEQ ID NO: 10; at least 9, preferably at least 10, more preferably at least 11, and most preferably at least 12 contiguous amino acids of SEQ ID NO: 4; and at least 23, preferably at least 24, more preferably at least 25, and most preferably at least 26 contiguous amino acids of SEQ ID NO: 12. Preferably the fragment or derivative of the TWIK channel protein is"functionally active"meaning that the TWIK channel protein derivative or fragment exhibits one or more functional activities associated with a full-length, wild-type TWIK channel protein comprising the amino acid sequence of any one of SEQ NOs: 2,4,6,8,10,12, and 14. As one example, a fragment or derivative may have antigenicity such that it can be used in immunoassays, for immunization, for inhibition of TWIK channel activity, etc, as discussed further below regarding generation of antibodies to TWIK channel proteins. For purposes herein, functionally active fragments also include those fragments that exhibit one or more structural features of a TWIK channel, such as a P or TM domain. Fragments or derivatives of TWIK channel proteins can be tested for functional activity by various procedures known in the art. The TWIK channel derivatives of the invention can be produced by various methods known in the art. The manipulations which result in their production can occur at the gene or protein level. For example, a cloned TWIK channel gene sequence can be cleaved at appropriate sites with restriction endonuclease (s) (Wells et al., Philos. Trans. R. Soc. London SerA (1986) 317: 415), followed by further enzymatic modification if desired, isolated, and ligated in vitro, and expressed to produce the desired derivative. Alternatively, a TWIK channel gene can be mutated in vitro or in vivo, to create and/or destroy translation, initiation, and/or termination sequences, or to create variations in coding regions and/or to form new restriction endonuclease sites or destroy preexisting ones, to facilitate further in vitro modification. A variety of mutagenesis techniques are known in the art such as chemical mutagenesis, in vitro site-directed mutagenesis (Carter et al., Nucl. Acids Res. (1986) 13: 4331), use of TABS linkers (available from Pharmacia and Upjohn, Kalamazoo, MI), etc. At the protein level, manipulations include post translational modification, e. g. glycosylation, acetylation, phosphorylation, amidation, derivatization by known protecting/blocking groups, proteolytic cleavage, linkage to an antibody molecule or other cellular ligand, etc. Any of numerous chemical modifications may be carried out by known technique (e. g. specific chemical cleavage by cyanogen bromide, trypsin, chymotrypsin, papain, V8 protease, NaBH4, acetylation, formylation, oxidation, reduction, metabolic synthesis in the presence of tunicamycin, etc.). Derivative proteins can also be chemically synthesized by use of a peptide synthesizer, for example to introduce nonclassical amino acids or chemical amino acid analogs as substitutions or additions into the TWIK channel protein sequence. Chimeric or fusion proteins can be made comprising an TWIK channel protein or fragment thereof (preferably consisting of at least a domain or motif of the TWIK channel protein) joined at its amino-or carboxy-terminus via a peptide bond to an amino acid sequence of a different protein. Such a chimeric protein can be produced by any known method, including: recombinant expression of a nucleic acid encoding the protein (comprising a TWIK channel-coding sequence joined in-frame to a coding sequence for a different protein); ligating the appropriate nucleic acid sequences encoding the desired amino acid sequences to each other in the proper coding frame, and expressing the chimeric product; and protein synthetic techniques, e. g. by use of a peptide synthesizer. ANTIBODIES TO TWIK CHANNEL PROTEINS TWIK channel proteins, including functional derivatives and fragments thereof (e. g. a TWIK channel protein encoded by a sequence of any one of SEQ ID NOs: 2,4,6,8,10,12, and 14, or a subsequence thereof) may be used as an immunogen to generate monoclonal or polyclonal antibodies and antibody fragments or derivatives (e. g. chimeric, single chain, Fab fragments). For example, antibodies to a particular domain of an TWIK channel protein may be desired (e. g. a P or TM domain). In a specific embodiment, fragments of a TWIK channel protein identified as hydrophilic are used as immunogens for antibody production using artknown methods. Various known methods for antibody production can be used including cell culture of hybridomas; production of monoclonal antibodies in germ-free animals (PCT/US90/02545); the use of human hybridomas (Cole et al., PNAS (1983) 80: 2026-2030; Cole et al., in Monoclonal Antibodies and Cancer Therapy (1985) Alan R. Liss, pp. 77-96), and production of humanized antibodies (Jones et al., Nature (1986) 321: 522-525; U. S. Pat. 5,530,101). In a particular embodiment, TWIK polypeptide fragments provide specific antigens and/or immunogens, especially when coupled to carrier proteins. For example, peptides are covalently coupled to keyhole limpet antigen (KLH) and the conjugate is emulsified in Freund's complete adjuvant. Laboratory rabbits are immunized according to conventional protocol and bled. The presence of specific antibodies is assayed by solid phase immunosorbent assays using immobilized corresponding polypeptide. Specific activity or function of the antibodies produced may be determined by convenient in vitro, cell-based, or in vivo assays: e. g. in vitro binding assays, etc. Binding specificity may be assayed by binding equilibrium constants (usually at least about 107 M-1, preferably at least about 108 M-', more preferably at least about 109 M-1). IDENTIFICATION OF PROTEINS THAT INTERACT WITH TWIK CHANNELS The present invention provides methods of identifying or screening for molecules, such as proteins or other compounds, which interact with TWIK channel proteins, or derivatives, or fragments thereof. Assays to find interacting proteins can be performed by any method known in the art, for example, immunoprecipitation with an antibody that binds to the protein in a complex followed by analysis by size fractionation of the immunoprecipitated proteins (e. g. by denaturing or nondenaturing polyacrylamide gel electrophoresis), Western analysis, nondenaturing gel electrophoresis, etc. A preferred method for identifying interacting proteins is a two hybrid assay system or variation thereof (Fields and Song, Nature (1989) 340: 245-246; U. S. Pat. No. 5, 283,173; for review see Brent and Finley, Annu. Rev. Genet. (1997) 31: 663-704). The most commonly used two-hybrid screen system is performed using yeast. All systems share three elements: 1) a gene that directs the synthesis of a"bait"protein fused to a DNA binding domain; 2) one or more"reporter"genes having an upstream binding site for the bait, and 3) a gene that directs the synthesis of a"prey"protein fused to an activation domain that activates transcription of the reporter gene. For the screening of proteins that interact with TWIK channel proteins, the"bait"is preferably a TWIK channel protein, expressed as a fusion protein to a DNA binding domain; and the"prey"protein is a protein to be tested for ability to interact with the bait, and is expressed as a fusion protein to a transcription activation domain. In one embodiment, the prey proteins can be obtained from recombinant biological libraries expressing random peptides. The bait fusion protein can be constructed using any suitable DNA binding domain, such as the E. coli LexA repressor protein, or the yeast GAL-4 protein (Bartel et al., BioTechniques (1993) 14: 920-924, Chasman et al., Mol. Cell. Biol. (1989) 9: 4746-4749; Ma et al., Cell (1987) 48: 847-853; Ptashne et al., Nature (1990) 346: 329-331). The prey fusion protein can be constructed using any suitable activation domain such as GAL-4, VP-16, etc. In various embodiments the preys contain useful moieties such as nuclear localization signals (Ylikomi et al., EMBO J. (1992) 11: 3681-3694; Dingwall and Laskey, Trends Biochem. Sci. Trends Biochem. Sci. (1991) 16: 479-481) or epitope tags (Allen et al., Trends Biochem. Sci. Trends Biochem. Sci. (1995) 20: 511-516) to facilitate isolation of the encoded proteins. Any reporter gene can be used that has a detectable phenotype. In various specific embodiments, some reporter genes allow cells expressing them to be selected by growth on appropriate medium (e. g. HIS3, LEU2 described by Chien et al., PNAS (1991) 88: 9572-9582; and Gyuris et al., Cell (1993) 75: 791-803). Others allow cells expressing them to be visually screened such as LacZ and GFP (Chien et al., supra; and http:/www. biolOl. com), etc. Although the preferred host for two-hybrid screening is the yeast, the host cell in which the interaction assay and transcription of the reporter gene occurs can be any cell, such as mammalian (e. g. monkey, mouse, rat, human, bovine), chicken, bacterial, or insect cells. Various vectors and host strains for expression of the two fusion protein populations in yeast can be used (U. S. Pat. No. 5,468,614; Bartel et al., Cellular Interactions in Development (1993) Hartley, ed., Practical Approach Series xviii, IRL Press at Oxford University Press, New York, NY, pp. 153-179; and Fields and Sternglanz, Trends In Genetics (1994) 10: 286-292). As an example of a mammalian system, interaction of activation tagged VP16 derivatives with a GAL4-derived bait drives expression of reporters that direct the synthesis of Hygromycin B phosphotransferase, Chloramphenicol acetyltransferase, or CD4 cell surface antigen (Fearon et al., PNAS (1992) 89: 7958-7962). In another embodiment, interaction of VP16-tagged derivatives with GAL-4-derived baits drives the synthesis of SV40 T antigen, which in turn promotes the replication of the prey plasmid, which carries an SV40 origin (Vasavada et al., PNAS (1991) 88: 10686-10690). In a preferred embodiment, the bait TWIK channel gene and the prey library of chimeric genes are combined by mating the two yeast strains on solid or liquid media for a period of approximately 6-8 hours. The resulting diploids contain both kinds of chimeric genes, i. e., the DNA-binding domain fusion and the activation domain fusion. Transcription of the reporter gene can be detected by a linked replication assay, for example, as described by Vasavada et al., supra, or using immunoassay methods, preferably as described in Alam and Cook (Anal. Biochem. (1990) 188: 245-254). The activation of other reporter genes like URA3, HIS3, LYS2, or LEU2 enables the cells to grow in the absence of uracil, histidine, lysine, or leucine, respectively, and hence serves as a selectable marker. Other types of reporters are monitored by measuring a detectable signal. For example, GFP and lacZ have gene products that are fluorescent and chromogenic, respectively. After interacting proteins have been identified, the DNA sequences encoding the proteins can be isolated. In one method, the activation domain sequences or DNA-binding domain sequences (depending on the prey hybrid used) are amplified, for example, by PCR using pairs of oligonucleotide primers specific for the coding region of the DNA binding domain or activation domain. Other known amplification methods can be used, such as ligase chain reaction, use of Q replicase, or various other methods described (see Kricka et al., Molecular Probing, Blotting, and Sequencing (1995) Academic Press, New York, Chapter 1 and Table IX). If a shuttle (yeast to E. coli) vector is used to express the fusion proteins, the DNA sequences encoding the proteins can be isolated by transforming the yeast DNA into E. coli and recovering the plasmids from E. coli. Alternatively, the yeast vector can be isolated, and the insert encoding the fusion protein subcloned into a bacterial expression vector, for growth of the plasmid in E. coli. It should be noted that one of the inefficiencies in the two-hybrid system is use of transmembrane portions of proteins in the bait or the prey fusions (Ausubel et al., supra; Allen et al., supra). Since most of the two-hybrid systems are engineered to enter the nucleus and activate transcription, use of transmembrane portions of proteins will interfere with proper association, folding, and nuclear transport of bait or prey segments for transcriptional activation. Since all proteins in the present invention are transmembrane proteins, a successful two-hybrid scheme for TWIK channel proteins will use non-membrane associated domains for bait. BIOCHEMICAL AND FUNCTIONAL ASSAYS USING TWIK CHANNEL PROTEINS TWIK channel proteins are useful for biochemical assays aimed at the identification and characterization of molecules that modulate the action of TWIK channel proteins and modify their properties as ion channels. The cDNAs encoding the TWIK channel proteins can be individually subcloned into any of a large variety of eukaryotic expression vectors permitting expression in insect and mammalian cells, described above. The resulting genetically engineered cell lines expressing TWIK channel proteins can be assayed for production, processing, and secretion of mature TWIK channel proteins, for example with antibodies to Drosophila, or Leptotarsa TWIK channel proteins and Western blotting assays, ELISA assays, or electrophysiology studies. The TWIK channel proteins, their derivatives, fragments, or domains, can be used in assays to identify molecules that would specifically bind to them. For assays specific to ion channels and their functional activation, one can employ either crude culture medium or extracts containing secreted protein from genetically engineered cells (devoid of other TWIK channel proteins), or partially purified culture medium or extracts, or preferably highly purified Drosophila TWIK channel protein fractionated, for example, by chromatographic methods. Alternatively, a mature TWIK channel protein can be synthesized using chemical methods (Nagata et al., Peptides (1992) 13 (4): 653-662). IDENTIFICATION OF TWIK BINDING PROTEINS The functional activity of TWIK proteins, derivatives and fragments can be assayed by various methods known to one skilled in the art (Current Protocols in Protein Science (1998) Coligan et al., eds., John Wiley & Sons, Inc., Somerset, New Jersey). For example, various immunoassays are available for testing the ability of a protein to bind to or compete with a wildtype TWIK protein for binding to an anti-TWIK protein antibody. Suitable assays include radioimmunoassays, ELISA (enzyme linked immunosorbent assay),"sandwich"immunoassays, immunoradiometric assays, gel diffusion precipitin reactions, immunodiffusion assays, in situ immunoassays (e. g., using colloidal gold, enzyme or radioisotope labels), western blots, precipitation reactions, agglutination assays (e. g., gel agglutination assays, hemagglutination assays), complement fixation assays, immunofluorescence assays, protein A assays, and immunoelectrophoresis assays, etc. In one embodiment, antibody binding is detected by detecting a label on the primary antibody. In another embodiment, the primary antibody is detected by detecting binding of a secondary antibody or reagent to the primary antibody. In a further embodiment, the secondary antibody is labeled. Other assays would include binding assays between a TWIK, its binding protein, its substrates, or receptors, where such molecules are identified. Finally, function of a TWIK gene can be assayed by mis-expressing a wild-type or mutant TWIK gene that encodes the TWIK gene protein in a transgenic animal by driving expression with a homologous or heterologous promoter; and detecting a phenotype in the transgenic animal, so as to study the function of the TWIK gene. TWIK GENE REGULATORY ELEMENTS TWIK gene regulatory DNA elements such as enhancers or promoters, can be assayed to identify tissues, cells, genes and factors that specifically control TWIK protein production. Analyzing components that are specific to TWIK protein function can lead to an understanding of how to manipulate these regulatory processes, especially for pesticide and therapeutic applications, as well as an understanding of how to diagnose dysfunction in these processes. In a specific embodiment, gene fusions with the TWIK regulatory elements can be made. For compact genes that have relatively few and small intervening sequences, such as those described herein for Drosophila, or Leptinotarsa, it is typically the case that the regulatory elements that control spatial and temporal expression patterns are found in the DNA immediately upstream of the coding region, extending to the nearest neighboring gene. Regulatory regions can be used to construct gene fusions where the regulatory DNAs are operably fused to a coding region for a reporter protein whose expression is easily detected, and these constructs are introduced as transgenes into the animal of choice. An entire regulatory DNA region can be used, or the regulatory region can be divided into smaller segments to identify sub-elements that might be specific for controlling expression a given cell type or stage of development. Examples of reporter proteins that can be used for construction of these gene fusions include E. coli beta-galactosidase or green fluorescent protein (GFP) whose products can be detected readily in situ and that are useful for histological studies (O'Kane and Gehring PNAS (1987) 84 (24): 9123-9127; Chalfie et al., Science (1994) 263: 802-805) and sorting of specific cells that express TWIK proteins (Cumberledge and Krasnow (1994) Methods in Cell Biology 44: 143-159); the cre or FLP recombinase proteins that can be used to control the presence and expression of other genes in the same cells through site-specific recombination (Golic and Lindquist (1989) Cell 59 (3): 499-509; White et al., Science (1996) 271: 805-807); toxic proteins such as the reaper and hid cell death proteins, which are useful to specifically ablate cells that normally express TWIK proteins in order to assess the physiological function of the cells (Kingston, In Current Protocols in Molecular Biology (1998) Ausubel et al., John Wiley & Sons, Inc. sections 12.0.3-12.10) or any other protein where it is desired to examine the function this particular protein specifically in cells that synthesize TWIK proteins. Alternatively, a binary reporter system can be used, similar to that described above, where the TWIK regulatory element is operably fused to the coding region of an exogenous transcriptional activator protein, such as the GAL4 or tTA activators described above, to create an TWIK regulatory element"driver gene". For the other half of the binary system the exogenous activator controls a separate"target gene"containing a coding region of a reporter protein operably fused to a cognate regulatory element for the exogenous activator protein, such as UASG or a tTA-response element, respectively. An advantage of a binary system is that a single driver gene construct can be used to activate transcription from preconstructed target genes encoding different reporter proteins, each with its own uses as delineated above. The TWIK regulatory element-reporter gene fusions described in the preceding paragraph are also useful for tests of genetic interactions, where the objective is to identify those genes that have a specific role in controlling the expression of TWIK genes, or promoting the growth and differentiation of the tissues that expresses the TWIK protein. In another specific embodiment, TWIK gene regulatory DNA elements are useful in protein-DNA binding assays to identify gene regulatory proteins that control the expression of TWIK genes. Such gene regulatory proteins can be detected using a variety of methods that probe specific protein-DNA interactions well known to those skilled in the art (Kingston, supra) including in vivo footprinting assays based on protection of DNA sequences from chemical and enzymatic modification within living or permeabilized cells, in vitro footprinting assays based on protection of DNA sequences from chemical or enzymatic modification using protein extracts nitrocellulose filter-binding assays and gel electrophoresis mobility shift assays using radioactively labeled regulatory DNA elements mixed with protein extracts. Candidate TWIK gene regulatory proteins can themselves be purified using a combination of conventional and DNA-affinity purification techniques. Molecular cloning strategies can also be used to identify proteins that specifically bind TWIK gene regulatory DNA elements. For example, a Drosophila cDNA library in an expression vector, can be screened for Drosophila cDNAs that encode TWIK gene regulatory element DNA-binding activity. Similarly, the yeast"one-hybrid" system can be used (Li and Herskowitz, Science (1993) 262: 1870-1874; Luo et al., Biotechniques (1996) 20 (4): 564-568; Vidal et al., PNAS (1996) 93 (19): 10315-10320). GENERATION AND GENETIC ANALYSIS OF ANIMALS AND CELL LINES WITH ALTERED EXPRESSION OF TWIK GENES Both genetically modified animal models (i. e. in vivo models), such as C. elegans and Drosophila, and in vitro models such as genetically engineered cell lines expressing or misexpressing TWIK pathway genes, are useful for the functional analysis of these channels. Such models that display detectable phenotypes, such as those described in more detail below, can be used for the identification and characterization of TWIK pathway genes or other genes of interest and/or phenotypes associated with the mutation or mis-expression of an TWIK pathway protein. The term"mis-expression"as used herein encompasses mis-expression due to gene mutations. Thus, a mis-expressed TWIK pathway protein may be one having an amino acid sequence that differs from wild-type (i. e. it is a derivative of the normal protein). A misexpressed TWIK pathway protein may also be one in which one or more amino acids have been deleted, and thus is a"fragment"of the normal protein. As used herein,"mis-expression"also includes ectopic expression (e. g. by altering the normal spatial or temporal expression), overexpression (e. g. by multiple gene copies), underexpression, non-expression (e. g. by gene knockout or blocking expression that would otherwise normally occur), and further, expression in ectopic tissues. As used in the following discussion concerning in vivo and in vitro models, the term"gene of interest"refers to an TWIK pathway gene (i. e. TWIK, TAP), or any other gene involved in regulation or modulation of the TWIK pathway. The in vivo and in vitro models may be genetically engineered or modified so that they 1) have deletions and/or insertions of one or more TWIK pathway genes, 2) harbor interfering RNA sequences derived from TWIK pathway genes, 3) have had one or more endogenous TWIK pathway genes mutated (e. g. contain deletions, insertions, rearrangements, or point mutations in an TWIK gene or genes), and/or 4) contain transgenes for mis-expression of wildtype or mutant forms of such genes. Such genetically modified in vivo and in vitro models are useful for identification of new genes that are involved in the synthesis, activation, control, etc. of TWIK pathway genes and/or gene products. The newly identified genes could constitute possible pesticide targets (as judged by animal model phenotypes such as non-viability, block of normal development, defective feeding, defective movement, or defective reproduction). The model systems can also be used for testing potential pesticidal or pharmaceutical compounds that interact with the TWIK pathway, for example by administering the compound to the model system using any suitable method (e. g. direct contact, ingestion, injection, etc.) and observing any changes in phenotype, for example defective movement, lethality, etc. Various genetic engineering and expression modification methods which can be used are known to one of ordinary skill in the art, including chemical mutagenesis, transposon mutagenesis, antisense RNA interference, and transgene-mediated mis-expression. GENERATING LOSS-OF-FUNCTION MUTATIONS BY MUTAGENESIS Loss-of-function mutations in an invertebrate metazoan TWIK gene can be generated by one of many mutagenesis methods known to investigators skilled in the art (Ashburner, In Drosophila melanogaster : A Laboratory Manual (1989), Cold Spring Harbor, NY, Cold Spring Harbor Laboratory Press: pp. 299-418; Fly pushing: The Theory and Practice of Drosophila melanogaster Genetics (1997) Cold Spring Harbor Press, Plainview, NY; The nematode C. elegans (1988) Wood, Ed., Cold Spring Harbor Laboratory Press, Cold Spring harbor, New York). Techniques for producing mutations in a gene or genome could include use of radiation ( e. g., X-ray, W, or gamma ray), or chemicals (e. g., EMS, MMS, ENU, formaldehyde, etc.). Other methods of altering expression of genes include use of transposons (e. g., P element, EP type"overexpression trap"element, mariner element, piggyBac transposon, hermes, minos, sleeping beauty, etc.), antisense, double-stranded RNA interference, peptide and RNA aptamers, directed deletions, homologous recombination, dominant negative alleles, and intrabodies. GENERATING LOSS-OF-FUNCTION PHENOTYPES USING RNA-BASED METHODS TWIK genes may be identified and/or characterized by generating loss-of-function phenotypes in animals of interest through RNA-based methods. Loss-of-function phenotypes can be generated by antisense RNA methods (Schubiger and Edgar, Methods in Cell Biology (1994) 44: 697-713). One form of the antisense RNA method involves the injection of embryos with an antisense RNA that is partially homologous to the gene-of-interest (in this case a TWIK gene). Another form of the antisense RNA method involves expression of an antisense RNA partially homologous to the gene-of-interest by operably joining a portion of the gene-ofinterest in the antisense orientation to a powerful promoter that can drive the expression of large quantities of antisense RNA, either generally throughout the animal or in specific tissues. Antisense RNA-generated loss-of-function phenotypes have been reported previously for several Drosophila genes including cactus, pecanex, and Kriippel (LaBonne et al., Dev. Biol. (1989) 136 (1): 1-16; Schuh and Jackle, Genome (1989) 31 (1): 422-425; Geisler et al., Cell (1992) 71 (4): 613-621). Loss-of-function phenotypes can also be generated by cosuppression methods (Bingham Cell (1997) 90 (3): 385-387; Smyth, Curr. Biol. (1997) 7 (12): 793-795; Que and Jorgensen, Dev. Genet. (1998) 22 (1): 100-109). Cosuppression is a phenomenon of reduced gene expression produced by expression or injection of a sense strand RNA corresponding to a partial segment of the gene-of-interest. Cosuppression effects have been employed extensively in plants to generate loss-of-function phenotypes, but there is only a single report of cosuppression in Drosophila where reduced expression of the Adh gene was induced from a white-Adh transgene (Pal-Bhadra et al., Cell (1997) 90 (3): 479-490). Another method for generating loss-of-function phenotypes is by double-stranded RNA interference (dsRNAi). This method is based on the interfering properties of double-stranded RNA derived from the coding regions of gene, and has proven to be of great utility in genetic studies of C. elegans (Fire et al., Nature (1998) 391: 806-811), and can also be used to generate loss-of-function phenotypes in Drosophila (Kennerdell and Carthew, Cell (1998) 95: 1017-1026; Misquitta and Patterson PNAS (1999) 96: 1451-1456). In this method, complementary sense and antisense RNAs derived from a substantial portion of a gene of interest, such as a sensitizer or TWIK gene, are synthesized in vitro. The resulting sense and antisense RNAs are annealed in an injection buffer, and the double-stranded RNA injected or otherwise introduced into animals (such as in their food or by soaking in the buffer containing the RNA). Progeny of the injected animals are then inspected for phenotypes of interest. GENERATING LOSS-OF-FUNCTION PHENOTYPES USING PEPTIDE AND RNA APTAMERS Another method for generating loss-of-function phenotypes is the use of peptide aptamers, which are peptides or small polypeptides that act as dominant inhibitors of protein function. Peptide aptamers specifically bind to target proteins, blocking their ability to function (Kolonin and Finley, PNAS (1998) 95: 14266-14271). Due to the highly selective nature of peptide aptamers, they may be used not only to target a specific protein, but also to target specific functions of a given protein. Further, peptide aptamers may be expressed in a controlled fashion by use of promoters which regulate expression in a temporal, spatial or inducible manner. Peptide aptamers act dominantly; therefore, they can be used to analyze proteins for which loss-of-function mutants are not available. Peptide aptamers that bind with high affinity and specificity to a target protein may be isolated by a variety of techniques known in the art. In one method, they are isolated from random peptide libraries by yeast two-hybrid screens (Xu et al., PNAS (1997) 94: 12473-12478). They can also be isolated from phage libraries (Hoogenboom et al., Immunotechnology (1998) 4: 1-20) or chemically generated peptides/libraries. RNA aptamers are specific RNA ligands for proteins, that can specifically inhibit protein function of the gene (Good et al., Gene Therapy (1997) 4: 45-54; Ellington. et al., Biotechnol. Annu. Rev. (1995) 1: 185-214). In vitro selection methods can be used to identify RNA aptamers having a selected specificity (Bell et al., J. Biol. Chem. (1998) 273: 14309-14314). RNA aptamers can be used to decrease the expression of an TWIK protein or derivative thereof, or a protein that interacts with the TWIK protein. GENERATING LOSS OF FUNCTION PHENOTYPES USING INTRABODIES Intracellularly expressed antibodies, or intrabodies, are single-chain antibody molecules designed to bind and inactivate target molecules inside cells. Intrabodies have been used in cell assays and in whole organisms such as Drosophila (Chen et al., Hum. Gen. Ther. (1994) 5: 595601; Hassanzadeh et al., Febs Lett. (1998) 16 (1,2): 75-80 and 81-86). In a preferred embodiment, inducible expression vectors are constructed with intrabodies that would react specifically with TWIK proteins. TRANSGENESIS Typically, transgenic animals are created that contain gene fusions of the coding regions of the TWIK pathway gene (from either genomic DNA or cDNA) operably joined to a specific promoter and transcriptional enhancer whose regulation has been well characterized, preferably heterologous promoters/enhancers (i. e. promoters/enhancers that are non-native to the TWIK pathway genes being expressed). Heat shock promoters/enhancers, useful for temperature induced mis-expression in Drosophila include the hsp70 and hsp83 genes, and in C. elegans, include hsp 16-2 and hsp 16-41. Tissue specific promoters/enhancers are also useful, and in Drosophila, include sevenless (Bowtell et al., Genes Dev. (1988) 2 (6): 620-634), eyeless (Bowtell et al., PNAS (1991) 88 (15): 6853-6857), and glass-responsive promoters/enhancers (Quiring et al., Science (1994) 265: 785-789) which are useful for expression in the eye; and enhancers/promoters derived from the dpp or vestigal genes which are useful for expression in the wing (Staehling-Hampton et al., Cell Growth Differ. (1994) 5 (6): 585-593; Kim et al., Nature (1996) 382: 133-138). Finally, where it is necessary to restrict the activity of dominant active or dominant negative transgenes to regions where the pathway is normally active, it may be useful to use endogenous promoters of genes in the pathway, such as the TWIK pathway genes. In C. elegans, examples of useful tissue specific promoters/enhancers include the myo-2 gene promoter, useful for pharyngeal muscle-specific expression; the hlh-1 gene promoter, useful for body-muscle-specific expression; and the mec-3 gene promoter, useful for touchneuron-specific gene expression. In a preferred embodiment, gene fusions for directing the misexpression of TWIK pathway genes are incorporated into a transformation vector which is injected into nematodes along with a plasmid containing a dominant selectable marker, such as rol-6. Transgenic animals are identified as those exhibiting a roller phenotype, and the transgenic animals are inspected for additional phenotypes of interest created by mis-expression of the TWIK pathway gene. In Drosophila, binary control systems that employ exogenous DNA are useful when testing the mis-expression of genes in a wide variety of developmental stage-specific and tissuespecific patterns. Two examples of binary exogenous regulatory systems include the UAS/GAL4 system from yeast (Hay et al., PNAS (1997) 94 (10): 5195-5200; Ellis et al., Development (1993) 119 (3): 855-865), and the"Tet system"derived from E. coli (Bello et al., Development (1998) 125: 2193-2202). The UAS/GAL4 system is a well-establi (Brand and Perrimon, Development (1993) 118 (2): 401-15). In this approach, transgenic Drosophila, termed"target"lines. are generated where the gene of interest to be mis-expressed is operably fused to an appropriate promoter controlled by UASG. Other transgenic Drosophila strains, termed"driver"lines, are generated where the GAL4 coding region is operably fused to promoters/enhancers that direct the expression of the GAL4 activator protein in specific tissues, such as the eye, wing, nervous system, gut, or musculature. The gene of interest is not expressed in the target lines for lack of a transcriptional activator to drive transcription from the promoter joined to the gene of interest. However, when the UAS-target line is crossed with a GAL4 driver line, mis-expression of the gene of interest is induced in resulting progeny in a specific pattern that is characteristic for that GAL4 line. The technical simplicity of this approach makes it possible to sample the effects of directed mis-expression of the gene of interest in a wide variety of tissues by generating one transgenic target line with the gene of interest, and crossing that target line with a panel of pre-existing driver lines. In the"Tet"binary control system, transgenic Drosophila driver lines are generated where the coding region for a tetracycline-controlled transcriptional activator (tTA) is operably fused to promoters/enhancers that direct the expression of tTA in a tissue-specific and/or developmental stage-specific manner. The driver lines are crossed with transgenic Drosophila target lines where the coding region for the gene of interest to be mis-expressed is operably fused to a promoter that possesses a tTA-responsive regulatory element. When the resulting progeny are supplied with food supplemented with a sufficient amount of tetracycline, expression of the gene of interest is blocked. Expression of the gene of interest can be induced at will simply by removal of tetracycline from the food. Also, the level of expression of the gene of interest can be adjusted by varying the level of tetracycline in the food. Thus, the use of the Tet system as a binary control mechanism for mis-expression has the advantage of providing a means to control the amplitude and timing of mis-expression of the gene of interest, in addition to spatial control. Consequently, if a gene of interest (e. g. a tumor suppressor gene) has lethal or deleterious effects when mis-expressed at an early stage in development, such as the embryonic or larval stages, the function of the gene of interest in the adult can still be assessed by adding tetracycline to the food during early stages of development and removing tetracycline later so as to induce mis-expression only at the adult stage. Transposon insertions lying adjacent to the TWIK gene of interest may be use to generate deletions of flanking genomic DNA, which if induced in the germline, are stably propagated in subsequent generations. The utility of this technique in generating deletions has been demonstrated in male Drosophila using P elements in a technique known as P-mediated male recombination (Preston and Engels, Genetics (1996) 144: 1611-1638). Dominant negative mutations, where a mutation to a gene creates an inactive protein, can result in loss-of-function or reduced-function phenotype even in the presence of a normal copy of the gene, can be made using known methods (Hershkowitz, Nature (1987) 329: 219-222). In the case of active monomeric proteins, over expression of an inactive form, achieved for example, by linking the mutant gene to a highly active promoter, can cause competition for natural substrates or ligands sufficient to significantly reduce net activity of the normal protein. Alternatively, changes to active site residues can be made to create a virtually irreversible association with a target. In the case of active multimeric proteins, several strategies can guide selection of a dominant negative mutant. In one embodiment, activity of a multmeric complex can be decreased by expression of genes coding exogenous protein fragments that bind to the association domains of the wild type proteins and prevent multimer formation. Alternatively, over-expression of an inactive protein unit can sequester wild-type active units in inactive multimers, and thereby decrease multimeric activity (Nocka et al., EMBO J. (1990) 9: 18051813). For example, in the case of multimeric DNA binding proteins, the DNA binding domain can be deleted, or the activation domain deleted. Also, in this case, the DNA binding domain unit can be expressed without the activation domain causing sequestering of the target DNA. Thereby, DNA binding sites are tied up without any possible activation of expression. In the case where a particular type of unit normally undergoes a conformational change during activity, expression of a rigid unit can also inactivate resultant complexes. It is also possible to replace an activation domain with a transcriptional repression domain and thus change a transcriptional activator into a transcriptional repressor. Transcriptional repression domains from the engrailed and Kruppel proteins have been used for such a purpose (Jaynes and O'Ferrell, EMBO J. (1991) 10: 1427-1433; Licht et al., PNAS (1993) 90: 11361-11365). ASSAYS FOR CHANGE IN GENE EXPRESSION Various expression analysis techniques may be used to identify genes which are differentially expressed between a cell line or an animal expressing a wild type TWIK gene compared to another cell line or animal expressing a mutant TWIK gene. Such expression profiling techniques include differential display, serial analysis of gene expression (SAGE), nucleic acid array technology, subtractive hybridization, and proteome analysis (e. g. mass spectrometry and two-dimensional protein gels). Nucleic acid array technology may be used to determine a global (i. e., genome-wide) gene expression pattern in a normal animal for comparison with an animal having a mutation in one or more TWIK gene. Gene expression profiling can also be used to identify other genes (or proteins) that may have a functional relation to (e. g. may participate in a signaling pathway with) or be a transcriptional target of an TWIK gene. The genes are identified by detecting changes in their expression levels following mutation, i. e., insertion, deletion or substitution in, or over-expression, under-expression, misexpression or knock-out, of a TWIK gene. PREDICTED PHENOTYPES ASSOCIATED WITH TWIK PATHWAY GENE MUTATIONS After isolation of model animals carrying mutated or mis-expressed TWIK pathway genes or inhibitory RNAs, animals are carefully examined for phenotypes of interest. For analysis of TWIK pathway genes that have been mutated (i. e. deletions, insertions, and/or point mutations) animal models that are both homozygous and heterozygous for the altered TWIK pathway gene are analyzed. Examples of specific phenotypes that may be investigated include lethality; sterility; feeding behavior, perturbations in neuromuscular function including alterations in motility, and alterations in sensitivity to pesticides and pharmaceuticals. Some phenotypes more specific to flies include alterations in: larval crawling, flight ability, walking, grooming and phototaxis, alterations in the responses of sensory organs, changes in the morphology, size or number of imaginal discs, eyes, wings, legs, bristles, antennae, gut, fat body, and musculature. Some phenotypes more specific to nematodes include: locomotory, egg laying, chemosensation, male mating, and intestinal expulsion defects. Genomic sequences containing an TWIK pathway gene can be used to confirm whether an existing mutant insect or worm line corresponds to a mutation in one or more TWIK pathway genes, by rescuing the mutant phenotype. Briefly, a genomic fragment containing the TWIK pathway gene of interest and potential flanking regulatory regions can be subcloned into any appropriate insect (such as Drosophila) or worm (such as C. elegans) transformation vector, and injected into the animals. For Drosophila, an appropriate helper plasmid is used in the injections to supply transposase. Resulting transformants are crossed for complementation testing to an existing panel of Drosophila or C. elegans lines whose mutations have been mapped to the vicinity of the gene of interest (Fly Pushing: The Theory and Practice of Drosophila Genetics, supra; and Caenorhabditis elegans: Modem Biological Analysis of an Organism (1995), Epstein and Shakes, eds.). If a mutant line is discovered to be rescued by this genomic fragment, as judged by complementation of the mutant phenotype, then the mutant line likely harbors a mutation in the TWIK pathway gene. This prediction can be further confirme by sequencing the TWIK pathway gene from the mutant line to identify the lesion in the TWIK pathway gene. IDENTIFICATION OF GENES THAT MODIFY TWIK GENES The characterization of new phenotypes created by mutations in TWIK genes enables one to test for genetic interactions between TWIK genes and other genes that may participate in the same, related, or interacting genetic or biochemical pathway (s). Individual genes can be used as starting points in large-scale genetic modifier screens as described in more detail below. Alternatively, RNAi methods can be used to simulate loss-of-function mutations in the genes being analyzed. It is of particular interest to investigate whether there are any interactions of TWIK genes with other well-characterized genes, particularly genes involved in ion transport. GENETIC MODIFIER SCREENS A genetic modifier screen using invertebrate model organisms is a particularly preferred method for identifying genes that interact with TWIK genes, because large numbers of animals can be systematically screened making it more that interacting genes will be identified. In C. elegans and Drosophila, a screen of up to about 10,000 animals is considered to be a pilot-scale screen. Moderate-scale screens usually employ about 10,000 to about 50,000 flies or up to about 100,000 worms, and large-scale screens employ greater than about 50,000 or 100,000 flies or worms, respectively. In a genetic modifier screen, animals having a mutant phenotype due to a mutation in one or more TWIK genes are further mutagenized, for example by chemical mutagenesis or transposon mutagenesis. The mutagenesis procedures used in typical genetic modifier screens of C. elegans are well known in the art. One method involves exposure of hermaphrodites that carry mutations in one or more TWIK genes to a mutagen, such as EMS or trimethylpsoralen with ultraviolet radiation (Huang and Stemberg, Methods in Cell Biology (1995) 48: 97-122). Alternatively, transposable elements are used, often by the introduction of a mutator locus, such as mut-2 or mut-7, which promotes mobility of transposons (Anderson, Methods in Cell Biology (1995) 4: 31-58). In Drosophila, the mutagenesis methods and other procedures used in a genetic modifier screen depend upon the precise nature of the mutant allele being modified; these methods are discussed in more detail below under the Drosophila genetic modifier screen subheading. Progeny of the mutagenized animals are generated and screened for the rare individuals that display suppressed or enhanced versions of the original mutant TWIK phenotype. Such animals are presumed to have mutations in other genes, called"modifier"genes, that participate in the same phenotype-generating pathway. The newly-identified modifier genes can be isolated away from the mutations in the TWIK genes by genetic crosses, so that the intrinsic phenotypes caused by the modifier mutations can be assessed in isolation. Modifier genes can be mapped using a combination of genetic and molecular methods known in the art. Modifiers that come from a genetic screen in C. elegans are preferably mapped with visible genetic markers and/or with molecular markers such as STS markers (The nematode C. elegans, supra, Caenorhabditis elegans: Modem Biological Analysis of an Organism, supra). Modifier genes may be uncovered by identification of a genomic clone which rescues the mutant phenotype. Alternatively, modifier genes that are identified by a Tcl- based screen can be uncovered using transposon display technology (Korswagen et al., PNAS (1996) 93: 14680-14685). Standard techniques used for the mapping of modifiers that come from a genetic screen in Drosophila include meiotic mapping with visible or molecular genetic markers; complementation analysis with deficiencies, duplications, and lethal P-element insertions; and cytological analysis of chromosomal aberrations (Fly Pushing: Theory and Practice of Drosophila Genetics, supra; Drosophila: A Laboratory Handbook, supra). Genes corresponding to modifier mutations that fail to complement a lethal P-element may be cloned by plasmid rescue of the genomic sequence surrounding that P-element. Alternatively, modifier genes may be mapped by phenotype rescue and positional cloning (Sambrook et al., supra). Newly identified modifier mutations can be tested directly for interaction with other genes of interest known to be involved or implicated with TWIK genes using methods described above. Also, the new modifier mutations can be tested for interactions with genes in other pathways that are not believed to be related to ion transport (e. g. Notch in Drosophila, and lin 15 in C. elegans). New modifier mutations that exhibit specific genetic interactions with other genes implicated in ion transport, but not interactions with genes in unrelated pathways, are of particular interest. The modifier mutations may also be used to identify"complementation groups". Two modifier mutations are considered to fall within the same complementation group if animals carrying both mutations in trans exhibit essentially the same phenotype as animals that are homozygous for each mutation individually and, generally are lethal when in trans to each other (Fly Pushing: The Theory and Practice of Drosophila Genetics, supra). Generally, individual complementation groups defined in this way correspond to individual genes. When TWIK modifier genes are identified, homologous genes in other species can be isolated using procedures based on cross-hybridization with modifier gene DNA probes, PCRbased strategies with primer sequences derived from the modifier genes, and/or computer searches of sequence databases. For therapeutic applications related to the function of TWIK genes, human and rodent homologues of the modifier genes are of particular interest. For pesticide and other agricultural applications, homologues of modifier genes in insects and arachnids are of particular interest. Insects, arachnids, and other organisms of interest include, among others, Isopoda; Diplopoda; Chilopoda; Symphyla; Thysanura; Collembola; Orthoptera, such as Scistocerca spp; Blattoidea, such as Blattella germanica; Dermaptera; Isoptera; Anoplura; Mallophaga; Thysanoptera; Heteroptera; Homoptera, including Bemisia tabaci, and Myzus spp.; Lepidoptera including Plodia interpunctella, Pectinophora gossypiella, Plutella spp., Heliothis spp., and Spodoptera species; Coleoptera such as Leptinotarsa, Diabrotica spp., Anthonomus spp., and Tribolium spp.; Hymenoptera, including Apis mellifera; Diptera, including Anopheles spp.; Siphonaptera, including Ctenocephalides felis; Arachnida; and Acarinan, including Amblyoma americanum; and nematodes, including Meloidogyne spp., and Heterodera glycinii. GENETIC MODIFIER SCREENS IN DROSOPHILA The procedures involved in typical Drosophila genetic modifier screens are well-known in the art (Wolfner and Goldberg, Methods in Cell Biology (1994) 44: 33-80; and Karim et al., Genetics (1996) 143: 315-329). The procedures used differ depending upon the precise nature of the mutant allele being modified. If the mutant allele is genetically recessive, as is commonly the situation for a loss-of-function allele, then most typically males, or in some cases females, which carry one copy of the mutant allele are exposed to an effective mutagen, such as EMS, MMS, ENU, triethylamine, diepoxyalkanes, ICR-170, formaldehyde, X-rays, gamma rays, or ultraviolet radiation. The mutagenized animals are crossed to animals of the opposite sex that also carry the mutant allele to be modified. In the case where the mutant allele being modified is genetically dominant, as is commonly the situation for ectopically expressed genes, wild type males are mutagenized and crossed to females carrying the mutant allele to be modified. The progeny of the mutagenized and crossed flies that exhibit either enhancement or suppression of the original phenotype are immediately crossed to adults containing balancer chromosomes and used as founders of a stable genetic line. In addition, progeny of the founder adult are retested under the original screening conditions to ensure stability and reproducibility of the phenotype. Additional secondary screens may be employed, as appropriate, to confirm the suitability of each new modifier mutant line for further analysis. Although the above-described Drosophila genetic modifier screens are quite powerful and sensitive, some genes that interact with TWIK channel genes may be missed in this approach, particularly if there is functional redundancy of those genes. This is because the vast majority of the mutations generated in the standard mutagenesis methods will be loss-of- function mutations, whereas gain-of-function mutations that could reveal genes with functional redundancy will be relatively rare. Another method of genetic screening in Drosophila has been developed that focuses specifically on systematic gain-of-function genetic screens (Rorth et al., Development (1998) 125: 1049-1057). This method is based on a modular mis-expression system utilizing components of the GAL-4/UAS system (described above) where a modified P element, termed an"enhanced P" (EP) element, is genetically engineered to contain a GAL-4responsive UAS element and promoter. Any other transposons can also be used for this system. The resulting transposon is used to randomly tag genes by insertional mutagenesis (similar to the method of P element mutagenesis described above). Thousands of transgenic Drosophila strains, termed EP lines, can be generated, each containing a specific UAS-tagged gene. This approach takes advantage of the preference of P elements to insert at the 5'-ends of genes. Consequently, many of the genes that are tagged by insertion of EP elements become operably fused to a GAL-4-regulated promoter, and increased expression or mis-expression of the randomly tagged gene can be induced by crossing in a GAL-4 driver gene. Systematic gain-of-function genetic screens for modifiers of phenotypes induced by mutation or mis-expression of a TWIK gene can be performed by crossing several thousand Drosophila EP lines individually into a genetic background containing a mutant or misexpressed TWIK gene, and further containing an appropriate GAL-4 driver transgene. It is also possible to remobilize the EP elements to obtain novel insertions. The progeny of these crosses are then analyzed for enhancement or suppression of the original mutant phenotype as described above. Those identified as having mutations that interact with the TWIK can be tested further to verify the reproducibility and specificity of this genetic interaction. EP insertions that demonstrate a specific genetic interaction with a mutant or mis-expressed TWIK gene, have a physically tagged a new gene which can be identified and sequenced using PCR or hybridization screening methods, allowing the isolation of the genomic DNA adjacent to the position of the EP element insertion. IDENTIFICATION OF COMPOUNDS WITH BINDING CAPACITY Proteins and other compounds that bind to, or otherwise directly interact with TWIK genes and proteins can be identified by screening methodologies that are well known in the art (see e. g., PCT International Publication No. WO 96/34099). The proteins and compounds include endogenous cellular components that interact with the identified genes and proteins in vivo and may provide new targets for pharmaceutical and therapeutic interventions. Other recombinant, synthetic, and otherwise exogenous compounds may have binding capacity and, therefore, may be candidates for pharmaceutical agents. For example, cell lysates or tissue homogenates may be screened for proteins or other compounds that bind to one of the normal or mutant TWIK genes and proteins. Any of a variety of exogenous compounds, both naturally occurring and/or synthetic (e. g., libraries of small molecules or peptides, or phage display libraries), may be screened for binding capacity. In a typical binding experiment a TWIK protein or fragment is mixed with test compounds under conditions conducive to binding for sufficient time for any binding to occur, and assays are performed to test for bound complexes. IDENTIFICATION OF POTENTIAL PESTICIDE OR DRUG TARGETS Once TWIK channel genes or TWIK channel interacting genes are identified, they can be assessed as potential pesticide or drug targets. As used herein, the term"pesticide"refers generally to chemical compounds that kill, paralyze, sterilize or otherwise disable pest species in the areas of agricultural crop protection, human and animal health. Exemplary pest species include parasites and disease vectors such as mosquitoes, fleas, ticks, parasitic nematodes, chiggers, mites, etc. Pest species also include those that are eradicated for aesthetic and hygienic purposes (e. g. ants, cockroaches, clothes moths, flour beetles, etc.), home and garden applications, and protection of structures (including wood boring pests such as termites, and marine surface fouling organisms). Pesticidal compounds can include traditional small organic molecule pesticides (typified by compound classes such as the organophosphates, pyrethroids, carbamates, organochlorines, benzoylureas, etc.) as well as proteinaceous toxins (such as the Bacillus thuringiensis Crytoxins (Gill et al., Annu Rev Entomol (1992) 37: 615-636) and Photorabdus luminescens toxins (Bowden et al., Science (1998) 280: 2129-2132). The pesticides or small molecules can be delivered by a variety of means such as direct application of the protein or nucleic acid encoding the protein, viral infection, and transgenic plants expressing the toxin in their tissues. Pesticides, drugs, and small molecules can be applied onto whole insects, nematodes, and other small invertebrate metazoans, and the ability of the compounds to modulate (e. g. block or enhance) TWIK channel activity can be observed. Alternatively, the effect of various compounds on TWIK channels can be assayed using cells that have been engineered to express one or more TWIK channels and associated proteins. Assays of compounds on worms: In a typical worm assay, the compounds to be tested are diluted in DMSO or other organic solvent, mixed with a bacterial solution, preferably OP50 strain of bacteria (Brenner, Genetics (1974) 110: 421-440), and supplied as food to the worms. The population of worms to be treated can be synchronized larvae (Sulston and Hodgkin, in The nematode C. elegans (1988), supra) or adults. Further, compounds can be added directly to the plate media (e. g. agar), or worm assays can be performed in liquid culture that contain the compound of interest (The nematode C. elegans, supra, Caenorhabditis elegans: Modem Biological Analysis of an Organism, supra). Adult and larval worms are treated with different concentrations of compounds, typically ranging from 1 mg/ml-0.001 mg/ml. Behavioral aberrations, such as a decrease in motility and growth, and morphological aberrations, sterility, and death are examined in both acutely and chronically treated adult and larval worms. For the acute assay, larval and adult worms are examined immediately after application of the compound and re-examined periodically (every 30 minutes) for 5-6 hours. Chronic, or long-term assays, are also performed on worms and the behavior of the treated worms are examined every 8-12 hours for 4-5 days. In some circumstances, it is necessary to reapply the pesticide to the treated worms every 24 hours for maximal effect. Assays of compounds on insects: Potential insecticidal compounds can be administered to insects in a variety of ways, including orally (including addition to synthetic diet, application to plants or prey to be consumed by the test organism), topically (including spraying, direct application of compound to animal, allowing animal to contact a treated surface), or by injection. Insecticides are typically very hydrophobic molecules and must commonly be dissolved in organic solvents, which are allowed to evaporate in the case of methanol or acetone or at low concentrations can be included to facilitate uptake (ethanol, dimethyl sulfoxide). The first step in an insect assay is the determination of the minimal lethal dose (MLD) on the insects after a chronic exposure to the compounds. The compounds are usually diluted in DMSO, and applied to the food surface bearing 0-48 hour old embryos and larvae. In addition to MLD, this step allows the determination of the fraction of eggs that hatch, behavior of the larvae, such as how they move/feed compared to untreated larvae, the fraction that survive to pupate, and the fraction that eclose (emergence of the adult insect from puparium). Based on these results more detailed assays with shorter exposure times may be designed, and larvae might be dissected to look for obvious morphological defects. Once the MLD is determined, more specific acute and chronic assays can be designed. In a typical acute assay, compounds are applied to the food surface for embryos, larvae, or adults, and the animals are observed after 2 hours and after an overnight incubation. For application on embryos, defects in development and the percent that survive to adulthood are determined. For larvae, defects in behavior, locomotion, and molting may be observed. For application on adults, behavior and neurological defects are observed, and effects on fertility are noted. For a chronic exposure assay, adults are placed on vials containing the compounds for 48 hours, then transferred to a clean container and observed for fertility, neurological defects, and death. Assay of compounds on cell cultures: Compounds that modulate (e. g. block or enhance) TWIK channel activity may also be assayed using cell culture. For example, the effect of exogenously added compounds cells expressing TWIK channels may be screened for their ability to modulate the activity of TWIK genes based upon measurements of intracellular potassium ion levels or regulation. Since TWIK channels are integral membrane proteins which serve as ion channels, the compounds may be screened for their ability to modulate TWIK-related potassium ion transport by measurements of ion channel fluxes and/or transmembrane voltage or current fluxes using patch clamp, voltage clamp and fluorescent dyes sensitive to intracellular calcium or transmembrane voltage. Ion channel function can also be assayed using transcriptional reporters, altered localization of protein, or by measurements of activation of second messengers such as cyclic AMP, cGMP tyrosine kinases, phosphates, increases in intracellular potassium ion levels, etc. Recombinantly made proteins may also be reconstructed in artificial membrane systems to study ion channel conductance and, therefore, the cells employed in such assays may comprise an artificial membrane or cell. Assays for changes in ion regulation or metabolism can be performed on cultured cells expressing endogenous normal or mutant TWIKs. Such studies also can be performed on cells transfected with vect EXAMPLES The following examples show how the nucleic acid sequences of SEQ ID NOs 1,3,5,7, 9,11, and 13 were isolated. An example of how these sequences and derivatives and fragments thereof can be used in compound screening assays is also provided. These examples are provided merely as illustrative of various aspects of the invention and should not be construed to limit the invention in any way. EXAMPLE 1: PREPARATION OF CDNA LIBRARIES Drosophila Library A Drosophila expressed sequence tag (EST) cDNA library was prepared as follows. *Tissue from mixed stage embryos (0-20 hour), imaginal disks and adult fly heads were collected and total RNA was prepared. Mitochondrial rRNA was removed from the total RNA by hybridization with biotinylated rRNA specific oligonucleotides and the resulting RNA was selected for polyadenylated mRNA. The resulting material was then used to construct a random primed library. First strand cDNA synthesis was primed using a six nucleotide random primer. The first strand cDNA was then tailed with terminal transferase to add approximately 15 dGTP molecules. The second strand was primed using a primer which contained a Notl site followed by a 13 nucleotide C-tail to hybridize to the G-tailed first strand cDNA. The double stranded cDNA was ligated with BstXl adaptors and digested with Notl. The cDNA was then sized on an agarose gel and the cDNA greater than 700 bp was purified. The cDNA was then ligated with Notl, BstXl digested pCDNA-sk+ vector (a derivative of pBluescript, Stratagene) and transformed into bacterial cells (XLlblue). The final complexity of the library was 6 X 106 independent clones. The cDNA library was normalized using a modification of a previously described method (Bonaldo et al., Genome Research (1996) 6: 791-806). A biotinylated driver was prepared from the cDNA by PCR amplification of the inserts and allowed to hybridize with single stranded plasmids of the same library. The resulting double-stranded forms were removed using strepavidin magnetic beads, the remaining single stranded plasmids were converted to double stranded molecules using Sequenase (Amersham, Arlington Hills, IL), and the plasmid DNA stored at-20 C prior to transformation. Aliquots of the normalized plasmid library were transformed into bacteria (XLlblue or DHIOB), plated at moderate density, and the colonies picked into a 384-well master plate containing bacterial growth media using a Qbot robot (Genetix, Christchurch, UK). The clones were allowed to grow for 24 hours at 37 C then the master plates were frozen at-80 C for storage. The total number of colonies picked for sequencing from the normalized library was 240,000. The master plates were used to inoculate media for growth and preparation of DNA for use as template in sequencing reactions. The reactions were primarily carried out with primer that initiated at the 5'end of the cDNA inserts. However, a minor percentage of the clones were also sequenced from the 3'end. Clones were selected for 3'end sequencing based on either further biological interest or the selection of clones that could extend assemblies of contiguous sequences ("contigs") as discussed below. Sequencing reactions were carried out on ABI377s and used either ABI FS, dirhodamine or BigDye chemistries (Applied Biosystems, Inc., Foster City, CA). Analysis of sequences were done as follows: the traces generated by the automated sequencers were base-called using the program"Phred" (Gordon, Genome Res. (1998) 8: 195202), which also assigned quality values to each base. The resulting sequences were trimmed for quality in view of the assigned scores. Vector sequences were also removed. Each sequence was compared to all other fly EST sequences using the BLAST program and a filter to identify regions of near 100% identity. Sequences with potential overlap were then assembled into contigs using the program"Phrap" (Phil Green, University of Washington, Seattle, Washington; http://bozeman. mbt. washington. edu/phrap. docs/phrap. html). The resulting assemblies were then compared to existing public databases and homology to known proteins was then used to direct translation of the consensus sequence. Where no BLAST homology was available, the statistically most likely translation based on codon and hexanucleotide preference was used. The Pfam (Bateman et al., Nucleic Acids Res. (1999) 27: 260-262) and Prosite (Hofmann et al., Nucleic Acids Res. (1999) 27 (1): 215-219) collection protein domains were used to identify motifs in the resulting translations. The contigs were placed in a database (FlyTagTM, Exelixis Pharmaceuticals, Inc., South San Francisco, CA) Leptinotarsa Library The Leptinotarsa cDNA library was prepared using the Lambda ZAP cDNA cloning kit (Stratagene, cat&num;200450) following manufacturer's protocols. The original cDNA used to construct the library was oligo-dt primed using mRNA from mixed stage larvae Colorado Potato Beetle. All colony picking, sequencing, and the data analysis were performed as described above for the Drosophila library. The resulting contigs were placed in a database (ColTagTM, Exelixis Pharmaceuticals, Inc.). EXAMPLE 2: CLONING AND ANALYSIS OF TWIK NUCLEIC ACID SEQUENCES The cloning of each of the TWIK nucleic acid sequences is described below. Upon completion of cloning, the sequences were analyzed using the Pfam and Prosite programs. The features of each sequence are outlined in Table 2 below. In addition, each completed sequence was searched using BLAST against the GenBank database (http://www. ncbi. nlm. nih. gov/Web/Search/index. html) to find the most similar DNA and protein sequences. The results of this search are outlined in Table 3. Unless otherwise noted, the PCR conditions used for cloning each TWIK nucleic acid sequence were as follows: A denaturation step of 94 C, 5 min; followed by 35 cycles of : 94 C 1 min, 55 C 1 min 72 C 1 min; then, a final extension at 72 C 10 min. All PCR primers encompassed the highly conserved P domains of TWIK nucleic acid sequences to help distinguish them from other potassium channels. All DNA sequencing reactions were performed using standard protocols for the BigDye sequencing reagents (Applied Biosystems, Inc.) and products were analyzed using ABI 377 DNA sequencers. Trace data obtained from the ABI 377 DNA sequencers was analyzed and assembled into contigs using the Phred-Phrap programs. 11 nucleic acid sequences below are shown in 5'to 3'orientation. TWIK2 TWIK2 was discovered as a sequenced, large-insert PI clone from the Berkeley Drosophila PI library (PI D205 = DS02368, AC004313, GenBank id no. ("GI") 3006211) and deposited by the Berkeley Drosophila Genome Project, BDGP (http://www. fruitfly. org). This sequence was not annotated. The cDNA sequence was predicted using Genscan sequence prediction program (Burge & Karlin, J. Mol. Biol. (1997) 268: 78-94). The full-length cDNA clone was produced by Rapid Amplification of cDNA ends (RACE) (Frohman et al., PNAS (1988) 85: 8998-9002). A RACE-ready library was generated from Clontech (Palo Alto, CA) Drosophila embryo polyA+ RNA (Cat&num; 6947-1) using Clontech's Marathon cDNA amplification kit (Cat&num; K1802 1), and following manufacturer's protocols. The following PCR primers were used on the library to retrieve full-length clones: TWIK2F2: TGGCTAAATGACGAGCACGAGCAC SEQ ID NO : 15 TWIK2R5: CAGTCCTCCTCTCTCATGTTGTGG SEQ ID NO : 16 TWIK2F6: ACAGGTGCATTGCCTATCTCATCT SEQ: 17 TWIK2R4: CGCGTTACGGTAAATTCGATTG SEQ ID NO : 18 PCR conditions were as follows: An initial denaturation step at 94 C for 2.5 min, followed by 30 cycles of 95 C, 40 sec; 68 C, 5 min, and a final extension at 72 C for 7 min. Products of PCR reactions were fractionated on a 1 % agarose gel, and purified from the gel using Qiagen (Valencia, CA) gel extraction kit following manufacturer's directions. The purified products were subject to a further round of PCR reactions, using only primers TWIK2F2/TWIK2R4. Products of this reaction were fractionated on a gel. The largest product was gel-purified and subcloned using Invitrogen's (Carlsbad, CA) TA cloning kit, following manufacturer's protocols. The obtained clones were then sequenced, and the final data resulted in a 3 kb contiguous sequence ("contig"). The predicted protein sequence of TWIK2 was analyzed using BLAST against known protein databases. The longest contiguous stretch of amino acid identity between TWIK2 and prior art sequences was 7, shared with C. elegans clone F31D4.7 (GI 3876514); the longest stretch of contiguous amino acid sequence similarity was 14, shared with the same clone. TWIK3 TWIK3 was discovered as two independent EST clones found in the Exelixis FlyTagTM cDNA database, as described above. PCR using conserved sequences in the ESTs was used to probe the Berkeley Drosophila PI library (From BDGP, and available from Research Genetics (Huntsville, AL, http://www. resgen. com) to obtain large insert Pl clones covering the region, and also to obtain cytological information. 5'and 3'RACE reactions were employed to obtain full-length cDNA clones. The following primers were used to perform PCR on Drosophila genomic DNA: TWIK3. F1: TTACGACGACGATGACTCTATG SEQ ID NO : l9 TWIK3. R1: AATCTTTAGTTCAAGTGCAGGTTT SEQ ID NO: 20 TWIK5. F1: CTCCACTGCTCCGATGTCCGAACT SEQ ID NO: 21 TWIK5. R1: CAACCGAGCGGCAAATTAGCCAA SEQ ID NO : 22 The PCR products were fractionated on a 1 % agarose gel, gel-purified, and then quantified with the aid of Hoefer DynaQuant 200 fluorometer (Amersham, Piscataway, NJ). A total of 50 ng of each product was then used as a probe for hybridization onto P 1 library filters. Each probe was labeled with a-dCTP 32P using Amersham's"redi-prime kit"as suggested by manufacturer. Labeled probes were then cleaned according to specifications with Pharmacia "probe-quant"columns. Counts were determined using a scintillation counter with counts ranging from 9x10 5-1x10 6 cpm. Probes were boiled for 10 min. at 100 C and quickly added to pre-warmed (65 C) hybridization buffer (5xSSPE, SxDenhardt's solution, 0.5% SDS, 0.1 mg/ml fish DNA) which was subsequently added to library filters and hybridized overnight at 65 C. Washes were performed the next day: 2 changes of O. 1xSSC, 0.1% SDS at room temperature for at least 15 min. each. 2 changes of O. lxSSC, 0.1% SDS at 65 C for at least 30 min. each. The membranes were then exposed to BioMax autoradiography X-ray film (Kodak, Rochester, NY) with two intensifying screens at-80 C for two days. The P1 filter produced 4 positive clones. Comparison of these clones to the BDGP database revealed all to map to a contig, Aprt, mapped to cytological band 6 1 F3 62B 11. PCR was then used using the same conditions and primers as before to verify the clones. Clones were propagated as described by Sambrook et al., supra. Genomic PI clones in this contig have been sequenced by the BDGP. The full-length cDNAs for each were obtained by RACE. The starting materials, as well as the protocols, were the same as those mentioned in the previous section. The following primers were used for RACE reactions on the EST clones believed to cover the 5'and the 3' portion of the TWIK gene coding region, respectively: TWIK 3: 5'EST: 5'RACE TWK5-R4: TTGCCGGATCCCTGTTCTACTCGA SEQ ID NO : 23 3'RACE TWK5-F4: TGCGTCGTCGGACAGTAGCCAGAT SEQIDNO: 24 TWIK 3: 3'EST 5'RACE TWK3-R4: CAAATCCGATTGTTGTCAGTGT SEQ ID NO : 25 3'RACE TWK3-F4: GAACACACTTTGAAAGATGGATA SEQ ID NO : 26 PCR conditions were as follows: an initial denaturation step of 95 C for 1 min, followed by 30 cycles of 95 C for 30 sec, 60 C for 30 sec, and 68 C for 3 min. The products of the PCR reactions were separated on a 1 % agarose gel, and purified from the as mentioned above. The major reaction products were subcloned into the vector pCRII using Invitrogen's TA cloning kit, following manufacturer's protocols. Subsequent clones were sequenced with the above TWIK-specific primers, M 13 forward and M 13 reverse vector primers, and the following primers: TWK3-F1: TTACGACGACGATGACTCTATG SEQ ID NO: 27 TWK3-R2: CTCACTACCAGAAAGACGCATA SEQ ID NO: 28 TWK5-F1: CTCCACTGCTCCGATGTCCGAACT SEQ ID NO: 29 TWK5-R2: ATGACCCAACGGTCTGGGAATGAC SEQ ID NO: 30 The sequence information was used to produce an approximately 3 kb of a total contiguous cDNA clone, containing a 2.2 kb open reading frame (ORF). Two separate PCR reactions were then used to generate two overlapping fragments: an approximately 1.5 kb 5' SacII-SalI fragment and an approximately 1 kb 3'SalI-NotI site for assembly into a protein expression vector. The following primers were used in these reactions: TWK3-FFl-Sac: GTACATCCGCGGGAGGAGGCCAGAGGAGGGTGACCATG SEQ ID NO: 31 TWK3-RR2-SalI: GCGGTGGAGCATCATAGTCGGGAAGT SEQ ID NO: 32 TWK3-RRl-NotI: ACTAGTACTAGCGGCCGCCTAATCCTCATCCTGCTCGTCGTCATCA SEQ ID NO: 33 TWK3-FF2-Sall: ATCTTCCAAAGCGTCCAGAGAACTGC SEQ ID NO : 34 The reaction products TWK3-FFl-Sac/TWK3-RR2-SalI and TWK3-RRl-NotI/TWK3- FF2-SalI were fractionated on 1.2 % agarose gels, gel-purified, and cloned into pCRII vector using the TOPO TA kit (Invitrogen). Four independent clones were then isolated, DNA purified, and sequenced with M13 forward and reverse primers, TWK3-F1, TWK3-R2, TWK5- F1, TWK5-R2, TWK3-F4, TWK3-R4, TWK5-F4, and TWK5-R4 primers, and the following primers: TWK3-SF5: TCGCCGAAGGGAGCGGACTGAACG SEQ ID NO : 35 TWK3-SF6: GTCCATCGCCTATTGCTCGCTGTA SEQ ID NO : 36 TWK3-SR5: CCCTACTTCTCCCAGGTGCCGAGT SEQ ID NO : 37 TWK3-SF6: AGTAGGCGGAATCCAAGAAGGACC SEQ ID NO : 38 From the consensus sequence, one clone for each of the two fragments was digested with 1) SacII/SalI and 2) NotI/SalI, respectively. The two fragments were then directionally cloned into the expression vector p1E1-3 (Novagen Inc., Madison, WI) which had been digested with SacII/NotI and purified. The predicted protein sequence (SEQ ID NO: 4) of TWIK3 was analyzed using BLAST against known protein databases. The longest contiguous stretch of identical amino acid sequence was 8, shared with C. elegans clone C24H11 (GI 1694994); the longest contiguous stretch of similar amino acids was 16, shared with the same clone. TWIK4 TWIK4 was discovered as an EST clone found in the Exelixis FlyTagTM cDNA database, as described above. To obtain full-length cDNA clones, available cDNA libraries were screened. P 1 library filters were also screened to generate genomic coverage and cytological information. One oligo-dT-primed and one random-primed embryonic Drosophila cDNA libraries were kindly provided by Dr. Rubin (Berkeley Drosophila Genome Project, Rubin Lab, LSA Rm. 539, U. C. Berkeley, Berkeley, CA 94720-3200). The random-primed library was plated out at a"low density" (5,000 pfu/plate x 20 plates) and the oligo-dt library was plated out at "high density" (50,000 pfu/plate x 20 plates) according to published protocols (Sambrook et al., supra). Since the Drosophila genome is approximately 160 Mb and the clones are about 1 kb in length this should respectively provide 62.5x coverage and 625x coverage. Plaques were plated out as described by Sambrook et al., supra. Primers were made from the highly conserved P domains of TWIK4 to perform PCR reactions on Drosophila genomic DNA: TWIK4. Fl: CCTCACTGACGGTGATCACGACCA SEQ ID NO: 39 TWIK4. R1: CGCCCGAATGTTGTGAACGACCT SEQ ID NO: 40 PCR products were used as probes to hybridize onto library filters, as described above. Positive clones were picked, replated, and rescreened by hybridization as described above. Positive clones were picked and confirmed by PCR using the same primers and conditions for amplifying the original probes. The clones were then sequenced using T3 and T7 vector primers, PCR primers indicated before, and the following: TWIK4. F2: TGCCGACAGGGATAAGGTGGAGGT SEQ ID NO: 41 TWIK4. F3: CTGGTGCCAGGCGATCGTGTGATA SEQ ID NO: 42 TWIK4. F4: TTCGGTCGTTGGGAGGACTGGAAC SEQ ID NO: 43 TWIK4. R2: CGCCAATGTTGGACAGGTAGAGCA SEQ ID NO: 44 TWIK4. R3: AAGGACTTGGCCAGGACGTCGC SEQ ID NO: 45 TWIK4. R4: GGCAGATGCGACATAGGCACACCT SEQ ID NO : 46 The sequence data obtained resulted in a 1.7 kb contig, of which the ORF was about 1.2 kb in length. For genomic library screening the same PCR products for the hybridization of cDNA libraries were used for hybridization onto PI high density filters. The hybridizations produced 4 positive clones. Comparison of these clones to the BDGP database revealed all to map to contig Dm 0746, located on cytological band 44A1-44B2. Clones in this contig have been sequenced by the BDGP, so further genomic sequencing was not necessary. A BLAST comparison of the predicted TWIK4 amino acid sequence (SEQ ID NO: 6) with sequences deposited in the public databases revealed a longest contiguous stretch of identical amino acids of 7 amino acids, shared with C. elegans clone C24H11.8 (GI 3874493); the longest contiguous stretch of similar amino acids was 15, shared with the same clone. TWIK 5 TWIK 5 was discovered as unanalyzed genomic PI sequence found in BDGP database (Pls D345, D349, D355 = DS00191, DS00050, DS05369, AC005894, GI 3818342). The cDNA clone was predicted using Genscan. In order to obtain a full-length cDNA clone, cDNA libraries were screened. The PI (DS05369) genomic clone, located at cytological band 46B1- 46B2, was re-sequenced to verify the public sequences. cDNA library screening was performed as described above. The PCR primers were: TWIK5. F1: CGAACGCAACTGGACGAT SEQ ID NO: 47 TWIK5. R1: CGCACTGCTGGCAGATGG SEQ ID N0: 48 TWIK5. F2: GCAACTGTCCGCACGGAA SEQ ID NO: 49 TWIK5. R2: GGCAATGCGTTTGCACTT SEQ ID NO: 50 Three positive cDNA clones were identified. A comparison of the predicted TWIK5 amino acid sequence (SEQ ID NO: 8) with sequences deposited in the public databases revealed a longest contiguous stretch of identical amino acids of 7 amino acids, shared with mouse TREK1 potassium channel subunit (GI 4584799); and a longest similar stretch of 17 amino acids, shared with C. elegans clone C24H11.8 (GI 3874493). Subsequent to the cloning and initial BLAST analysis of TWIK5, a full-length, unannotated sequence that encodes TWIK5 was deposited in the public databases by the BDGP (GI 5052537). TWIK6 TWIK6 was discovered as an unannotated EST clone from the BDGP database. In order to obtain full-length clones, the available cDNA libraries were screened as described above. To obtain genomic clones both PI and BAC libraries (from the BDGP and also available from Research Genetics) were screened as described above. The following primers were used for screening cDNA libraries: TWIK6. F1: CACCATGACAACCATCGG SEQ ID NO: 51 TWIK6. R1: GGCATTCGTGATGGCTTC SEQ ID NO : 52 PI and BAC genomic library screening was carried out. The PI filter produced 2 positive clones while the BAC filter produced 7. The clones were verified by PCR. Comparison of the results to the BDGP databases did not reveal a cytological location. A BLAST comparison of the predicted TWIK6 amino acid sequence (SEQ ID NO: 9) with sequences deposited in the public databases revealed a longest contiguous stretch of identical amino acid sequence of 6 amino acids, shared with C. elegans clone T28A8.1 (GI 3880336); the longest stretch of contiguous similar amino acids was 14, also shared with the same clone. TWIK7 TWIK7 was discovered as an EST clone in the Exelixis FlyTagTM cDNA database, as described above. To obtain full-length clone, the available cDNA libraries were screened. To get genomic coverage and cytological location, both P1 and BAC libraries were screened. cDNA libraries were screened as described above, using the following primers: TWIK7. F1: GACCTCATCTGTGTTGTG SEQ ID NO: 53 TWIK7. R1: GAGGGCTGGAGCTACTTC SEQ ID NO: 54 TWIK7. F2: GCACATGGACGAGATGTT SEQ ID NO: 55 TWIK7. R2: CACATCGCCCTCCAGCTT SEQ ID NO: 56 Five positive cDNA clones were identified, and re-screened as described above. The clones were then sequenced, as described above, using T3 and T7 vector primers, PCR primers indicated above, and the following: TWIK7. F3: CAACATCTCGTCCATGTG SEQ ID NO: 57 TWIK7. F4: GAAGCTGGAGGGCGATGTG SEQ ID NO: 58 TWIK7. R3: CACAACACAGATGAGGTC SEQ ID NO : 59 TWIK7. R4: GAAGTAGCTCCAGCCCCTC SEQ ID NO : 60 These sequences produced a 2.0 kb contig, of which 1.2 kb constituted an ORF. Genomic screening was carried out. The PI filter produced 3 positive clones while the BAC filter produced 7. Comparison of these results with the databases from BDGP did not produce a cytological location. One PI clone was submitted for full-length sequencing. Subsequent to the above-described cloning of the TWIK7 coding region, an unfinished genomic sequence of a BAC clone covering the TWIK7 gene was entered in the public databases (AC007646, GI 4895159, BACR03J04=BAC D687). A comparison of the predicted TWIK 7 amino acid sequence (SEQ ID NO: 12) with sequences deposited in the public databases revealed a longest contiguous stretch of identical amino acid sequence of 22 amino acids, shared with Homo sapiens TWIK-related acid-sensitive K+ channel (GI 2465542); the longest contiguous stretch of similar amino acids was 32, shared with the same sequence. cpbTWIK1 The Leptinotarsa cpbTWIKI nucleic acid sequence was discovered as an EST clone in the Exelixis ColTag cDNA database, as described above. It was sequenced from the 5'end and then re-sequenced from both ends, but the sequence was not overlapping. Primers were made in the 5'and 3'ends to obtain overlapping sequences. The following primers were used for sequencing: CPBT. 5'A TGTGTAGCGGAGCAGCGGTTTT SEQ ID NO: 61 CPBT. 5'B AGCGGTTTTCAGTTACTTTGAGG SEQ ID NO: 62 CPBT. 5'C GCGGTTTTCAGTTACTTTGAGGC SEQ ID NO: 63 CPBT. 5'D GCACCTGAGGAACGGGCACTGAG SEQ ID NO: 64 CPBT. 3'A CCCGGAACTGGCTAACCTCACTT SEQ ID NO: 65 The sequence reactions produced a 1 kb contig representing the full-length sequence of cpbTWIKI. The translation of the nucleotide sequence was made by analyzing BLAST results. A comparison of the predicted cpbTWIKI amino acid sequence (SEQ ID NO: 14) with sequences deposited in the public databases revealed a longest contiguous stretch of identical amino acid sequence of 7 amino acids, shared with Orvctolagus cuniculus rabKCNKl (GI 2213891); the longest stretch of similar amino acids was 19, shared with the same sequence. FEATURES OF TWIK CHANNEL NUCLEIC ACID SEQUENCES Table II summarizes the features of the above-described TWIK channel nucleic acid sequences and their encoded proteins."NA"refers to nucleic acid and"AA"refers to amino acid. TABLE II EMI52.1 <tb> NAME <SEP> CODING <SEP> TRANS-TRANS-PORE <SEP> (P) <SEP> PORE <SEP> (P) <tb> <SEP> SEQUENCE <SEP> MEMBRANE <SEP> MEMBRANE <SEP> DOMAINS <SEP> DOMAINS <tb> <SEP> LENGTH <SEP> (TM) <SEP> DOMAINS <SEP> (TM) <SEP> (NA) <SEP> (AA) <tb> <SEP> (NA) <SEP> (NA) <SEP> DOMAINS <tb> <SEP> (AA) <tb> <SEP> TM1: <SEP> 1668-1716 <SEP> TM1: <SEP> 556-572 <tb> TWIK2 <SEP> 2988 <SEP> TM2: <SEP> 2028-2076 <SEP> TM2: <SEP> 676-692 <SEP> PI: <SEP> 1902-1971 <SEP> PI: <SEP> 634-657 <tb> <SEP> TM3: <SEP> 2412-2460 <SEP> TM3: <SEP> 804-820 <SEP> P2: <SEP> 2433-2499 <SEP> P2: <SEP> 811-833 <tb> <SEP> TM4: <SEP> 2568-2616 <SEP> TM4: <SEP> 856-872 <tb> <SEP> TM1: <SEP> 102-150 <SEP> TM1: <SEP> 34-50 <tb> TWIK3 <SEP> 2193 <SEP> TM2: <SEP> 507-555 <SEP> TM2: <SEP> 169-185 <SEP> P1: <SEP> 405-477 <SEP> P1: <SEP> 135-159 <tb> <SEP> TM3: <SEP> 1902-1950 <SEP> TM3: <SEP> 634-650 <SEP> P2: <SEP> 1938-2007 <SEP> P2: <SEP> 646-669 <tb> <SEP> TM4: <SEP> 2076-2124 <SEP> TM4: <SEP> 692-708 <tb> <SEP> TM1: <SEP> 102-150 <SEP> TM1: <SEP> 34-50 <tb> TWIK4 <SEP> 1188 <SEP> TM2: <SEP> 477-525 <SEP> TM2: <SEP> 159-175 <SEP> P1: <SEP> 381-453 <SEP> P1: <SEP> 127-151 <tb> <SEP> TM3: BLAST RESULTS FOR THE TWIK NUCLEIC ACID SEQUENCES Nucleotide and amino acid sequences for each of the TWIK nucleic acid sequences and their encoded proteins were searched against all available nucleotide and amino acid sequences in the public databases, using BLAST (Altschul et al., supra). Table 3 below summarizes the results. In each case, the 5 most similar sequences are listed. TABLE 3 EMI53.1 <tb> TWIK <SEP> DNA <SEP> BLAST <SEP> PROTEIN <SEP> BLAST <tb> <SEP> GI&num; <SEP> DESCRIPTION <SEP> GI&num; <SEP> DESCRIPTION <tb> TWIK2 <SEP> 3006211= <SEP> DS02368 <SEP> (P1 <SEP> D205) <SEP> 3876514 <SEP> F31D4.7 <tb> <SEP> AC004313 <SEP> Drosophila <SEP> (Z92832) <SEP> C. <SEP> elle <SEP> ans <SEP> clone <tb> <SEP> 1877065 <SEP> C. <SEP> elegans <SEP> clone <SEP> C18D11 <SEP> 4584799= <SEP> TREK-1 <SEP> K+ <SEP> channel <tb> <SEP> AAC53005 <SEP> subunit <SEP> Mus <SEP> musculus <tb> <SEP> (U73488) <tb> <SEP> 1694994 <SEP> C. <SEP> elegans <SEP> clone <SEP> C24H11 <SEP> 3808068 <SEP> Drosophila <SEP> two <SEP> P <tb> <SEP> domain <SEP> K+ <SEP> channel <tb> <SEP> ORK1 <tb> <SEP> 3150442 <SEP> AF033017 <SEP> Mus <SEP> musculus <SEP> 1916869 <SEP> TWIK-1 <SEP> K+ <SEP> channel <tb> <SEP> TWIK-1 <SEP> Mus <SEP> musculus <tb> <SEP> 1877088 <SEP> F14H10 <SEP> C. <SEP> elegans <SEP> clone <tb> <SEP> (Z92783) <tb> <SEP> 392542 <SEP> AF084830 <SEP> Homo <SEP> sapiens <tb> <SEP> two <SEP> pore <SEP> domain <SEP> K+ <tb> <SEP> channel, <SEP> TASK2 <tb> TWIK3 <SEP> 3779012= <SEP> Drosophila <SEP> DNA <SEP> 3924830= <SEP> Predicted <SEP> using <tb> <SEP> AC005847 <SEP> sequence <SEP> (Pls <SEP> DS03179 <SEP> CAA98957 <SEP> Genefinder; <SEP> similar <SEP> to <tb> <SEP> (D226), <SEP> DS06357 <SEP> (D230), <SEP> (Z74475) <SEP> K+ <SEP> channel <SEP> protein <SEP> [C. <tb> <SEP> DS03404 <SEP> (D231), <SEP> elegans] <tb> <SEP> DS06962 <SEP> (D232), <SEP> and <tb> <SEP> DS07291 <SEP> (D240)) <tb> <SEP> 416040 <SEP> Drosophila <SEP> kinesin-like <SEP> 4103376= <SEP> putative <SEP> K+ <SEP> channel <tb> <SEP> U01842 <SEP> protein <SEP> mRNA <SEP> AAD09338 <SEP> DP4 <SEP> [Mus <SEP> musculus] <tb> <SEP> (AF022821) <tb> <SEP> 4056406= <SEP> Drosophila <SEP> PI <SEP> clone <SEP> 4584799= <SEP> TREK-1 <SEP> K+ <SEP> channel <tb> <SEP> AC005473 <SEP> DS02142 <SEP> AAC53005 <SEP> subunit <SEP> [Mus <SEP> musculus] <tb> <SEP> (U73488) <tb> <SEP> 1772445= <SEP> Mus <SEP> musculus <SEP> mRNA <SEP> for <tb> <SEP> D87747 <SEP> murine <SEP> CXCR-4 <tb> <SEP> 2465543= <SEP> Mus <SEP> musculus <SEP> TWIK <tb> <SEP> AF006824 <SEP> related <SEP> acid-sensitive <SEP> K+ <tb> <SEP> channel <SEP> (TASK) <SEP> mRNA <tb> <SEP> 1877065= <SEP> C. <SEP> elegans <SEP> DNA <SEP> from <tb> <SEP> Z92826 <SEP> clone <SEP> C18D11 <tb> EMI54.1 <tb> <SEP> 1694994= <SEP> C. <SEP> elegans <SEP> cosmid <tb> <SEP> Z81475 <SEP> C24H11 <tb> TWIK4 <SEP> 4056406= <SEP> Drosophila <SEP> PI <SEP> clone <SEP> 3874493= <SEP> C. <SEP> elegans <SEP> clone <tb> <SEP> AC005473 <SEP> DS02142 <SEP> CAB03914 <SEP> C24H11.8 <tb> <SEP> (Z81475) <tb> <SEP> 3779012= <SEP> Drosophila <SEP> DNA <SEP> 3880336= <SEP> C. <SEP> elegans <SEP> clone <tb> <SEP> AC005847 <SEP> sequence <SEP> (Pls <SEP> DS03179 <SEP> CAB07286 <SEP> T28A8.1 <tb> <SEP> (D226), <SEP> DS06357 <SEP> (D230), <SEP> (Z92813) <tb> <SEP> DS03404 <SEP> (D231), <tb> <SEP> DS06962 <SEP> (D232), <SEP> and <tb> <SEP> DS07291 <SEP> (D240)) <tb> <SEP> 1869276= <SEP> F. <SEP> rubripes <SEP> GSS <SEP> 3452417= <SEP> Putative <SEP> K+ <SEP> channel <tb> <SEP> Z92062FR <SEP> sequence, <SEP> clone <SEP> AAC328631 <SEP> subunit <SEP> n2P38 <tb> <SEP> 0008252 <SEP> 190022bB9 <SEP> (AF083652) <SEP> C. <SEP> elegans <tb> <SEP> 3818343= <SEP> Drosophila <SEP> P1 <SEP> clone <SEP> 2429407= <SEP> Contains <SEP> similarity <SEP> to <tb> <SEP> AC005430 <SEP> DS04740 <SEP> AAC71151 <SEP> outward-rectifier <SEP> K+ <tb> <SEP> (AF025454) <SEP> channels <SEP> C. <SEP> elegans <tb> <SEP> 157452= <SEP> DROFSHA <SEP> Drosophila <SEP> 3924830= <SEP> Predicted <SEP> using <tb> <SEP> M23221 <SEP> fsh <SEP> membrane <SEP> protein <SEP> CAA98957 <SEP> Genefinder; <SEP> similar <SEP> to <tb> <SEP> (Z74475) <SEP> potassium <SEP> K+ <SEP> protein <tb> <SEP> C. <SEP> elegans <tb> TWIK5 <SEP> 3818342= <SEP> Drosophila <SEP> PI <SEP> clones <SEP> 4584799= <SEP> TREK-1 <SEP> K+ <SEP> channel <tb> <SEP> AC005894. <SEP> DS00050, <SEP> DS00191, <SEP> and <SEP> AAC53005 <SEP> subunit <SEP> [Mus <SEP> musculus] <tb> <SEP> DS05369 <SEP> (U73488) <tb> <SEP> 3261554= <SEP> Mycobacterium <SEP> 3874493= <SEP> C. <SEP> elegans <SEP> clone <tb> <SEP> AL022022. <SEP> tuberculosis <SEP> H37Rv <SEP> CAB03914 <SEP> C24H11.8 <tb> <SEP> 1 <SEP> MTV023 <SEP> complete <SEP> genome; <SEP> (Z81475) <tb> <SEP> segment <SEP> 148/162 <tb> <SEP> 210287 <SEP> Dissostichusmawsoni <SEP> 1405526 <SEP> C. <SEP> elegans <SEP> clone <tb> <SEP> U58944.1 <SEP> AFGP <SEP> antifreeze <SEP> R04F11.4 <tb> <SEP> DMU5894 <SEP> glycopeptide <SEP> polyprotein <tb> <SEP> 4 <SEP> precursor <SEP> gene <tb> <SEP> 1633571= <SEP> Kaposi's <SEP> sarcoma-3924830= <SEP> Predicted <SEP> using <tb> <SEP> U52064.1 <SEP> associated <SEP> herpes-like <SEP> CAA989571 <SEP> Genefinder; <SEP> similar <SEP> to <tb> <SEP> KSU52064 <SEP> virus <SEP> ORF73 <SEP> homolog <SEP> (Z74475) <SEP> potassium <SEP> channel <tb> <SEP> gene <SEP> Pç <tb> <SEP> 2065526= <SEP> Kaposi's <SEP> sarcoma-3880336= <SEP> C <SEP> elegans <SEP> clone <tb> <SEP> U75698.1 <SEP> associated <SEP> herpesvirus <SEP> CAB072861 <SEP> T28A8.1 <tb> <SEP> KSU75698 <SEP> long <SEP> unique <SEP> region <SEP> (Z92813) <tb> <SEP> TWIK6 <SEP> 3943225= <SEP> LP07049.5prime <SEP> LP <SEP> 3880336= <SEP> C. <SEP> elegans <SEP> clone <tb> <SEP> AI293818 <SEP> Drosophila <SEP> larval-early <SEP> el349878 <SEP> T28A8.1 <tb> <SEP> pupal <SEP> cDNA <SEP> clone <tb> <SEP> 1695114= <SEP> C. <SEP> elegans <SEP> cosmid <SEP> 465874= <SEP> C <SEP> elegans <SEP> TWK-8 <tb> <SEP> Z82073 <SEP> W06D12 <SEP> P34410 <SEP> protein <tb> <SEP> 1439623= <SEP> C. <SEP> elegans <SEP> cosmid <SEP> C52B9 <SEP> 1078847= <SEP> C. <SEP> elegans <SEP> f22b7.7 <tb> <SEP> U64598 <SEP> S44635 <SEP> protein <tb> <SEP> 1255391= <SEP> C. <SEP> elegans <SEP> cosmid <SEP> F20A1 <SEP> 156306 <SEP> C. <SEP> elegans <SEP> cosmid <tb> <SEP> U53150 <SEP> F22B7 <tb> EMI55.1 <tb> <SEP> 2653149= <SEP> C. <SEP> elegans <SEP> cosmid <SEP> 1613511= <SEP> SEQ4 <SEP> from <SEP> US <SEP> Pat. <tb> <SEP> Z82073 <SEP> W06D12 <SEP> AAB16491 <SEP> No. <SEP> 5559026 <tb> TWIK7 <SEP> 4895159= <SEP> Unfinished <SEP> BAC <SEP> clone <SEP> 2429407= <SEP> contains <SEP> similarity <SEP> to <tb> <SEP> AC007646 <SEP> BACR03J04= <SEP> AAC71151 <SEP> outward-rectifier <tb> <SEP> BAC <SEP> D687 <SEP> K+ <SEP> channels <SEP> [C. <tb> <SEP> elegans, <SEP> TWIK23] <tb> <SEP> 2465541= <SEP> Homo <SEP> sapiens <SEP> TWIK-3452417= <SEP> C. <SEP> elegans <SEP> putative <SEP> K+ <tb> <SEP> AF006823 <SEP> related <SEP> acid-sensitive <SEP> K+ <SEP> AAC328631 <SEP> channel <SEP> subunit <SEP> n2P38 <tb> <SEP> channel <SEP> (TASK) <SEP> mRNA <tb> <SEP> 3043543= <SEP> Mus <SEP> musculus <SEP> mRNA <SEP> for <SEP> 2465542= <SEP> Homo <SEP> sapiens <SEP> TWIK <tb> <SEP> AB008537 <SEP> cTBAK <SEP> AAC51777 <SEP> related <SEP> acid-sensitive <tb> <SEP> K+ <SEP> channel <tb> <SEP> 3149958= <SEP> Mus <SEP> musculus <SEP> mRNA <SEP> for <SEP> 2809391= <SEP> Rattus <SEP> norvegicus <tb> <SEP> AB013345 <SEP> cTBAK <SEP> AAC39952 <SEP> TWIK-related <SEP> acid <tb> <SEP> sensitive <SEP> K+ <SEP> channel <tb> <SEP> 2465543= <SEP> Mus <SEP> musculus <SEP> TWIK-3043544= <SEP> Mus <SEP> musculus <SEP> cTBAK <tb> <SEP> AF006824 <SEP> related <SEP> acid-sensitive <SEP> K+ <SEP> BAA25436 <tb> <SEP> channel <SEP> (TASK) <SEP> mRNA <tb> CpbTWIK <SEP> 4581226= <SEP> C. <SEP> elegans <SEP> DNA <SEP> clone <SEP> 2213891= <SEP> Oryctolagus <SEP> cuniculus <tb> 1 <SEP> AL020988 <SEP> Y80D3 <SEP> AAB61602 <SEP> rabKCNKl <tb> <SEP> 4581216= <SEP> C. <SEP> elegans <SEP> clone <SEP> Y39B6 <SEP> 2135518= <SEP> Homo <SEP> sapiens <SEP> inward <tb> <SEP> Z95399 <SEP> S65566 <SEP> rectifier <SEP> K+ <SEP> channel <tb> <SEP> TWIK-1 <tb> <SEP> 1503390= <SEP> Rattus <SEP> norvegicus <SEP> 1086491= <SEP> Homo <SEP> sapiens <SEP> TWIK-1 <tb> <SEP> C06614 <SEP> pancreatic <SEP> islet <SEP> cDNA <SEP> AAB01688 <tb> <SEP> 1916295= <SEP> Homo <SEP> sapiens <SEP> K+ <tb> <SEP> AAB51147 <SEP> channel <SEP> KCNO1 <tb> <SEP> 2811120= <SEP> Homo <SEP> sapiens <SEP> two <SEP> P <tb> <SEP> AAB97878 <SEP> domain <SEP> K+ <SEP> channel <tb> <SEP> subunit <tb> Table IV further summarizes the BLAST results for each TWIK channel amino acid sequence. The"% Identity"column indicates, for each TWIK channel amino acid sequence, the longest stretch of contiguous amino acids that is novel with respect to prior art sequences as determined by BLAST. Thus, for example, any contiguous stretch of 8 amino acids of the TWIK2 amino acid sequence (SEQ ID NO: 2) is novel over sequences in public databases. The "% Similarity"column shows the longest stretch of contiguous amino acids for which there are no sequences contained within public database sharing 100% sequence similarity. For example, for any contiguous stretch of 15 amino acids of the TWIK2 channel protein, there are no sequences in the public databases that share 100% sequence identity. TABLE IV EMI56.1 <tb> TWIK <SEP> 100% <SEP> Identity <SEP> Length <SEP> (x) <SEP> 100 <SEP> % <SEP> Similarity <SEP> Length <SEP> (y) <tb> TWIK <SEP> 2 <SEP> (SEQ <SEP> ID <SEP> NO: <SEP> 2) <SEP> 8 <SEP> 15 <tb> TWIK <SEP> 3 <SEP> (SEQ <SEP> ID <SEP> NO: <SEP> 4) <SEP> 9 <SEP> 17 <tb> TWIK <SEP> 4 <SEP> (SEQ <SEP> ID <SEP> NO: <SEP> 6) <SEP> 8 <SEP> 16 <tb> TWIK <SEP> 5 <SEP> (SEQ <SEP> ID <SEP> NO: <SEP> 8) <SEP> 8 <SEP> 18 <tb> TWIK <SEP> 6 <SEP> (SEQ <SEP> ID <SEP> NO: <SEP> 10) <SEP> 7 <SEP> 15 <tb> TWIK <SEP> 7 <SEP> (SEQ <SEP> ID <SEP> NO: <SEP> 12) <SEP> 23 <SEP> 33 <tb> cpbTWIKl <SEP> (SEQ <SEP> ID <SEP> NO: <SEP> 14) <SEP> 8 <SEP> 20 <tb> EXAMPLE 3: TWIK EXPRESSION ANALYSIS TWIK expression analysis was carried out by in situ hybridization to Drosophila embryonic and larval tissues for the Drosophila TWIKs, using the cDNAs to generate antisense probes on Drosophila embryos and larval tissue. Antisense DIG-labeled RNA probes were synthesized using the Roche (NJ) Dig RNA Labeling Kit and T7 RNA polymerase according to the in situ hybridization protocol of BDGP methods page (http://www. fruitfly. org/methods/). The results showed that TWIK2 is expressed in the progenitor and developing muscle cells of the embryo and larval musculature. TWIK3 is expressed in the developing esophagus and hindgut of the embryo. TWIK6 is expressed in a region of the gut, in band of cells around the larval proventriculus. This most likely corresponding to the described imaginal ring that will give rise to adult tissues. TWIK7 is highly expressed in neuronal tissues: during late differentiation of the embryonic central nervous system, throughout the larval CNS during I st instar and in the brains of 3rd instar larvae, particularly the optic lobes. EXAMPLE 4: COMPOUND SCREENING USING TWIK EXPRESSION SYSTEMS cDNAs encoding TWIK channels of interest are cloned into baculovirus-compatible vectors (e. g. pIE-1 series, Novagen, Madison, WI) or mammalian cell culture-compatible vectors (e. g. pCDNA, Invitrogen, Carlsbad, CA) using standard methods. The resultant constructs are transiently transfected into insect or mammalian cell cultures, respectively. The transiently transfected cell lines are typically used 24-48 hours following transfection for electrophysiology studies. Whole cell recordings, using the voltage clamp technique, are taken on the transfected cells and compared with recordings taken from cells transfected with vector only. The cells are injected with a current of designated intensity for brief periods (up to 200 milliseconds). A resultant current, generated by the cell in returning to the resting potential, is recorded. The amplitude and duration of this current indicates the presence of a functional channel in the transfected cells. Current injections are repeated with increasing amperage-the resultant channel-generated current should increase to reflect the increased injected current. A channel-blocking compound may then be applied to the cell culture in the concentration range of about lxlO-9to lx10-6 M to determine the effect on the channel activity. If the compound inhibits channel activity, a resultant current is not generated in response to the injected current. The compound may be washed out of the cell culture and another compound tested in series. In a second type of experiment, the resting potential of transfected cells is compared to that of control cells. For potassium leak channels e. g. the TWIKS, a depolarized resting potential is observed in the transfected cells. A series of compounds can then be tested for interactions with the expressed channel by applying each compound and measuring any resultant changes in cellular resting potential.

Claims: WHAT IS CLAIMED IS: 1. An isolated nucleic acid molecule of less than about 15 kb in size comprising a nucleic acid sequence selected from the group consisting of : (a) a nucleic acid sequence that encodes a polypeptide comprising at least x contiguous amino acids of any one of SEQ ID NOs: 2,4,6,8,10,12, and 14, wherein for each respective SEQ ID NO, x is the number of amino acids listed in the column entitled"100% identity length x"in Table 4; (b) a nucleic acid sequence that encodes a polypeptide comprising at least y amino acids that share 100% sequence similarity with y amino acids of any one of SEQ ID NOs: 2,4,6,8, 10,12, and 14, wherein for each respective SEQ ID NO, y is the number of amino acids listed in the column entitled"100% similarity lengthy"in Table 4; and (c) the complement of the nucleic acid sequence of (a) or (b). 2. The isolated nucleic acid molecule of Claim 1 which is capable of hybridizing to a nucleic acid sequence selected from the group consisting of SEQ ID NOs: 2,4,6,8,10,12, and 14, using hybridization conditions that comprise 6X SSC/0% formamide hybridization buffer at 25 C and 4X SSC wash buffer at 35 C. 3. The isolated nucleic acid molecule of Claim 1 wherein said nucleic acid sequence encodes at least 25 contiguous amino acids of any one of SEQ ID NOs: 2,4,6,8,10,12 and 14. 4. The isolated nucleic acid molecule of Claim 1 wherein said nucleic acid sequence encodes at least 50 contiguous amino acids of any one of SEQ ID NOs: 2,4,6,8,10,12, and 14. 5. The isolated nucleic acid molecule of Claim 1 wherein said nucleic acid sequence encodes the entire sequence of any one of SEQ ID NOs: 2,4,6,8,10,12, and 14. 6. The isolated nucleic acid molecule of Claim 1 wherein said nucleic acid sequence encodes at least one TWIK channel P domain or TM domain. 7. A vector comprising the nucleic acid molecule of Claim 1. 8. A host cell comprising the vector of Claim 7. 9. A process for producing a protein comprising culturing the host cell of Claim 8 under conditions suitable for expression of said protein and recovering said protein. 10. A purified protein prepared by the process of Claim 9. 11. A method for detecting a candidate molecule that interacts with a protein or fragment thereof, said method comprising contacting said protein or fragment with one or more candidate molecules, and detecting any interaction between said candidate molecules and said protein or fragment; wherein the amino acid sequence of said protein comprises an amino acid sequence selected from the group consisting of an amino acid sequence comprising at least x contiguous amino acids of any one of SEQ ID NOs: 2,4,6,8,10,12, and 14, wherein for each respective SEQ ID NO, x is the number of amino acids listed in the column entitled"100% identity length" in Table 4, and an amino acid sequence comprising at leasty amino acids that share 100% sequence similarity with y amino acids of any one of SEQ ID NOs: 2,4,6,8,10,12, and 14, wherein for each respective SEQ ID NO, y is the number of amino acids listed in the column entitled"100% similarity length"in Table 4. 12. The method of Claim 11 for identifying a molecule that binds to said protein, wherein said candidate molecules are contacted with said protein or fragment under conditions conducive to binding to said TWIK channel protein or fragment, said method comprising detecting any binding that occurs of said candidate molecules to said protein or fragment. 13. The method of Claim 11 wherein said candidate molecules are a putative pesticidal or pharmaceutical agent. 14. The method of Claim 11 wherein said contacting comprises administering said candidate molecules to cultured host cells that have been genetically engineered to express said protein. 15. The method of Claim 11 wherein said contacting comprises administering said candidate molecules to a metazoan invertebrate organism that has been genetically engineered to express a TWIK channel protein. 16. The method of Claim 15 wherein said candidate molecules are a putative pesticide and said detecting entails observing modulations of TWIK channel activity that result in organism lethality. 17. The method of Claim 15 wherein said organism is an insect. 18. A first animal that is an insect, coelomate or pseudocoelomate that has been genetically modified to express or mis-express a protein, or the progeny of said animal that has inherited said protein expression or mis-expression, wherein said protein comprises an amino acid sequence selected from the group consisting of an amino acid sequence comprising at least x contiguous amino acids of any one of SEQ ID NOs: 2,4,6,8,10,12, and 14, wherein for each respective SEQ ID NO, x is the number of amino acids listed in the column entitled"100% identity length"in Table 4, and an amino acid sequence comprising at least y amino acids that share 100% sequence similarity withy amino acids of any one of SEQ ID NOs: 2,4,6,8,10,12, and 14, wherein for each respective SEQ ID NO, y is the number of amino acids listed in the column entitled"100% similarity length"in Table 4. 19. A method for studying potassium channel activity comprising detecting the phenotype caused by the expression or mis-expression of said protein in the first animal of Claim 18. 20. The method of Claim 19 additionally comprising administering one or more candidate molecules to said first animal or its progeny and observing any changes in potassium channel activity of said animal or its progeny. 21. The method of Claim 19 additionally comprising observing a second animal having the same genetic modification as the first animal which causes said expression or mis-expression of said protein, and wherein said second animal additionally comprises a mutation in a gene of interest, wherein differences, if any, between the phenotype of the first animal and the phenotype of the second animal identifies the gene of interest as capable of modifying the function of the gene encoding said protein.

Inventors: FRANCIS-LANG HELEN L, GENDREAU STEVEN B, GILLETT LUCILE A, JACOBUS DENISE A, JESCHKE PETER, LUO YULING, MARGOLIS JONATHAN S, NAUEN RALF, REDDY BINDU P, TIETJEN KLAUS, WINSLOW JOHN W, FRANCIS-LANG, HELEN, L., GENDREAU, STEVEN, B., GILLETT, LUCILE, A., JACOBUS, DENISE, A., JESCHKE, PETER, LUO, YULING, MARGOLIS, JONATHAN, S., NAUEN, RALF, REDDY, BINDU, P., TIETJEN, KLAUS, WINSLOW, JOHN, W.
Applicants: GENOPTERA LLC, GENOPTERA, LLC
Application year: 2000
Main classification: C12N15
IPC codes: C07K14, C12N15