SHORT EXTERNAL GUIDE SEQUENCES

Abstract: External guide sequence (EGS) molecules for eukaryotic RNAse P are engineered to target efficient and specific cleavage of target RNA. Engineered RNA molecules are designed and synthesized which contain specific nucleotide sequences which enable an external guide sequence for RNAse P to preferentially bind to and promote RNAse P-mediated cleavage of target RNA molecules. Short External Guide Sequence (SEGS) molecules have been constructed that, when hybridized to a target molecule, provide a minimal structure recognized as a substrate by RNAse P. The SEGS/target structure is comprised of structures similar to the A stem and the T stem of a tRNA, the natural substrate of RNAse P. The SEGS makes up only half of these stem structures. The other half of the stem structures is provided by the target molecule. By allowing the target molecule to form more of the RNAse P substrate structure, the disclosed SEGS molecules can be significantly smaller than previous EGS molecules. This makes SEGS molecules especially useful as therapeutic agents since they are easier to manufacture and administer in quantity.

Description: SHORT EXTERNAL GUIDE SEQUENCES Background of the Invention This application is directed to methods and external guide sequence compositions designed to target cleavage of RNA by RNAse P. Ribonucleic acid (RNA) molecules can serve not only as carriers of genetic information, for example, genomic retroviral RNA and messenger RNA (mRNA) molecules and as structures essential for protein synthesis, for example, transfer RNA (tRNA) and ribosomal RNA (rRNA) molecules, but also as enzymes which specifically cleave nucleic acid molecules. Such catalytic RNA molecules are called ribozymes. The discovery of catalytic RNA, by Drs. Altaian and Cech, who were awarded the Nobel prize in 1989, has generated much interest in commercial applications, particularly in therapeutics (Airman, Proc. Natl. Acad. Sci. USA 90:10898-10900 (1993); Symons, Annu. Rev. Biochem. 61:641-671 (1992); Rossi et al., Antisense Res. Dev. , 1:285-288 (1991); Cech, Annu. Rev. Biochem. 59:543-568, (1990)). Several classes of catalytic RNAs (ribozymes) have been described, including intron-derived ribozymes (WO 88/04300; see also, Cech, T., Annu. Rev. Biochem. , 59:543-568, (1990)), hammerhead ribozymes (WO 89/05852 and EP 321021 by GeneShears), axehead ribozymes (WO 91/04319 and WO 91/04324 by Innovir). RNAse P Another class of ribozymes include the RNA portion of an enzyme, RNAse P, which is involved in the processing of transfer RNA (tRNA), a common cellular component of the protein synthesis machinery. Bacterial RNAse P includes two components, a protein (C5) and an RNA (Ml). Sidney Airman and his coworkers demonstrated that the Ml RNA is capable of functioning just like the complete enzyme, showing that in Escherichia coli the RNA is essentially the catalytic component, (Guerrier-Takada et al. , Cell 35:849-857 (1983)). In subsequent work, Dr. Altaian and colleagues developed a method for converting virtually any RNA sequence into a substrate for bacterial RNAse P by using an external guide sequence (EGS), having at its 5' terminus at least seven nucleotides complementary to the nucleotides 3' to the cleavage site in the RNA to be cleaved and at its 5' terminus the nucleotides NCCA (N is any nucleotide)(WO 92/03566 by Yale, and Forster and Altaian, Science 238:407-409 (1990)). Using similar principles, EGS/RNAse P-directed cleavage of RNA has been developed for use in eukaryotic systems, where the external guide sequence forms structures similar to the stem and loop structures of tRNA and where the substrate RNA hybridizes to ends of the EGS to form structures similar to the acceptor and D stems of tRNA (Yuan et al., Proc. Natl. Acad. Sci. USA 89:8006-8010 (1992); WO 93/22434 by Yale). It has subsequently been shown that EGS molecules for use with eukaryotic RNAse P need form only a structure similar to the T stem and loop of tRNA, where, again, the substrate RNA hybridizes to ends of the EGS to form structures similar to the acceptor and D stems of tRNA (WO 95/24489 to Yale). These EGS molecules are useful for promoting RNAse P-mediated cleavage of target RNA molecules. They are especially useful for in vivo use since only the relatively small EGS molecule need be administered. The catalytic RNAse P is already present and active in the cells of the animal or patient. Yuan and Airman, EMBO J 14:159-168 (1995), and Carrara et al, Proc. Natl. Acad. Sci. (USA) 92:2627-2631 (1995), later determined a minimal structure necessary for cleavage of a substrate by RNase P. It is an object of the present invention to provide a therapeutic targeted for treatment of viral diseases and diseases involving abnormal transcription products, and method of use thereof. It is another object of the present invention to provide short external guide sequences for RNase P, vectors encoding such short external guide sequences, and methods of use thereof. It is another object of the present invention to provide chemically modified short external guide sequences for RNAse P with enhanced resistance to nuclease degradation. It is another object of the present invention to provide methods of cleaving target RNA molecules promoted by short external guide sequences for RNAse P. It is a further object of the present invention to provide short external guide sequences for RNAse P specifically targeted against viruses such as hepatitis, vectors encoding such short external guide sequences, and methods of use thereof. Summary of the Invention External guide sequence (EGS) molecules for eukaryotic RNAse P are engineered to target efficient and specific cleavage of target RNA. They contain specific nucleotide sequences which enable an external guide sequence for RNAse P to preferentially bind to and promote RNAse P- mediated cleavage of target RNA molecules. Short External Guide Sequence (SEGS) molecules have been constructed that, when hybridized to a target molecule, provide a minimal structure recognized as a substrate by RNAse P. The small EGS/target structure includes structures similar to the A stem and the T stem of a tRNA, the natural substrate of RNAse P. The SEGS makes up only half of these stem structures. The other half of the stem structures is provided by the target molecule. By allowing the target molecule to form more of the RNAse P substrate structure, the disclosed SEGS molecules can be significantly smaller than previous EGS molecules. This makes SEGS molecules especially useful as therapeutic agents since they are easier and less expensive to manufacture and administer in quantity. Chemically modified versions of these SEGS molecules having modified nucleotides or nucleotide linkages are designed to enhance their resistance to nuclease degradation. Specific regions are modified to achieve enhanced stability while maintaining RNAse P targeting activity. Examples demonstrate that SEGS molecules for RNAse P have been constructed that bind to and promote RNAse P cleavage of hepatitis viral RNA. Methods for the determination of the activity of an SEGS, for the purpose of construct- screening, as well as methods for using and producing such RNA molecules, are also disclosed. Brief Description of the Drawings Figure 1 is a diagram of the structure of a Short External Guide Sequence (SEGS) hybridized to a target RNA molecule. The parts of the SEGS (SEQ ID NO. 6) and target RNA molecule (SEQ ID NO. 7), with each serving a specific structural role in the SEGS/target RNA complex. The parts of the SEGS are, from 5' to 3', the T recognition arm and the A recognition arm. The parts of the target RNA are, from 5' to 3', the first target region, the bulge region, the second target region, and the turn region. The primary structural relationship between the SEGS and the target RNA is that the A recognition arm is complementary to the first target region and the T recognition arm is complementary to the second target region. Except for two of the nucleotides in the turn region, the sequences shown are merely examples and are not critical to obtaining RNAse P-mediated cleavage of target RNA in general. In this example, the target RNA is HBV RNA. Figure 2 is a diagram of the structure of a SEGS (EGS 3; SEQ ID NO. 1) and a short model target RNA (T 10) with the nucleotide sequence SEQ ID NO. 2. The two oligonucleotides are aligned to show the base pairing which forms a structure similar to the A stem and T stem of tRNA. This structure is recognized by eukaryotic RNAse P and promotes RNAse P- mediated cleavage of the target RNA. The RNAse P cleavage site is indicated with an arrow. Figure 3 is a diagram of the structure of a SEGS (EGS a) with the nucleotide sequence SEQ ID NO. 3 and a short model target RNA (T a) with the nucleotide sequence shown in nucleotides 1 to 36 of SEQ ID NO. 4. The two oligonucleotides are aligned to show the base pairing which forms a structure similar to the A stem and T stem of tRNA. This structure is recognized by eukaryotic RNAse P and promotes RNAse P-mediated cleavage of the target RNA. The RNAse P cleavage site is indicated with an arrow. Part of the model target RNA matches a portion of HBV sequence. The sequence involved in the "broken" T loop are the same as the sequences in the T loop of tRNA Tyr . Figure 4 is a diagram of the structure of EGS a with the nucleotide sequence SEQ ID NO. 3 and a short model target RNA (T a') with tae nucleotide sequence SEQ ID NO. 4. The two oligonucleotides are aligned to show the base pairing which forms a structure similar to the A stem and T stem of tRNA. This structure is recognized by eukaryotic RNAse P and promotes RNAse P-mediated cleavage of the target RNA. The RNAse P cleavage site is indicated with an arrow. The model target RNA matches a portion of HBV sequence. Figure 5 is a diagram of the structure of EGSs and a target RNA. On the left is shown tae structure of the 15 nucleotide SEGS (EGS 3; SEQ H> NO. 1) hybridized to Λe short model target RNA (T 7; SEQ ID NO. 2). On the right is shown the structure of Λe 12 nucleotide SEGS (EGS 7; nucleotides 4 to 15 of SEQ ID NO. 1) hybridized to Λe short model target RNA (T 7; SEQ ID NO. 2). The SEGS and target RNA are aligned to show Λe base pairing which forms a structure similar to Λe A stem and T stem of tRNA. This structure is recognized by eukaryotic RNAse P and promotes RNAse P-mediated cleavage of Λe target RNA. The RNAse P cleavage site is indicated wiΛ an arrow. Figure 6 is a diagram of Λe structure of a minimal RNAse P substrate which is similar to an SEGS/target RNA complex. The nucleotide sequence of Λe substrate is SEQ ID NO. 5. This structure is recognized and cleaved by eukaryotic RNAse P. The RNAse P cleavage site is indicated wiΛ an arrow. The sequence is model on a portion of HBV sequence. Figure 7 is a diagram of Λe structure formed by hybridization of a SEGS (HBV B) wiΛ Λe nucleotide sequence SEQ ID NO. 6 to a portion HBV RNA corresponding to nucleotides 375-424 of a 2.1 kb HBV RNA (SEQ ID NO. 7). The SEGS and HBV RNA are aligned to show the base pairing which forms a structure similar to Λe A stem and T stem of tRNA. The RNAse P cleavage site is indicated wiΛ an arrow. Figure 8 is a diagram of Λe structure formed by hybridization of a SEGS (HBV C) wiΛ Λe nucleotide sequence SEQ ID NO. 8 to a portion HBV RNA corresponding to nucleotides 543-598 of a 2.1 kb HBV RNA (SEQ ID NO. 9). The SEGS and HBV RNA are aligned to show Λe base pairing which forms a structure similar to Λe A stem and T stem of tRNA. The RNAse P cleavage site is indicated wiΛ an arrow. Figure 9 is a diagram of Λe structure formed by hybridization of a SEGS (HBV FI) wiΛ Λe nucleotide sequence SEQ ID NO. 10 to a portion HBV RNA corresponding to nucleotides 673-718 of a 2.1 kb HBV RNA (SEQ ID NO. 11). The SEGS and HBV RNA are aligned to show Λe base pairing which forms a structure similar to Λe A stem and T stem of tRNA. The RNAse P cleavage site is indicated wiΛ an arrow. Figure 10 is a diagram of Λe structure formed by hybridization of a SEGS (HBV H) wiΛ Λe nucleotide sequence SEQ ID NO. 12 to a portion HBV RNA corresponding to nucleotides 1559-1606 of a 2.1 kb HBV RNA (SEQ ID NO. 13). The SEGS and HBV RNA are aligned to show Λe base pairing which forms a structure similar to Λe A stem and T stem of tRNA. The RNAse P cleavage site is indicated wiΛ an arrow. Figure 11 is a diagram of Λe structure formed by hybridization of a SEGS (HBV HI) wiΛ Λe nucleotide sequence SEQ ID NO. 14 to a portion HBV RNA corresponding to nucleotides 1562-1606 of a 2.1 kb HBV RNA (nucleotides 4-48 of SEQ ID NO. 13). The SEGS and HBV RNA are aligned to show Λe base pairing which forms a structure similar to Λe A stem and T stem of tRNA. The RNAse P cleavage site is indicated wiΛ an arrow. Figure 12 is a diagram of the structure of a minimal RNAse P substrate which is similar to an SEGS/target RNA complex. The nucleotide sequence of Λe substrate is SEQ ID NO. 15. This structure is recognized and cleaved by eukaryotic RNAse P. The RNAse P cleavage site is indicated wiΛ an arrow. The sequences involved in Λe stems and in Λe T loop are Λe same as Λe sequences in Λe A stem and T stem and loop of tRNA Tyr . Figure 13 is a diagram of the structure of a SEGS (EGS 3) wiΛ Λe nucleotide sequence SEQ ID NO. 1 and a short model target RNA (T 7) wiΛ Λe nucleotide sequence shown in nucleotides 1 to 36 of SEQ ID NO. 2. The two oligonucleotides are aligned to show the base pairing which forms a structure similar to Λe A stem and T stem of tRNA. This structure is recognized by eukaryotic RNAse P and promotes RNAse P-mediated cleavage of Λe target RNA. The RNAse P cleavage site is indicated wiΛ an arrow. The sequences involved in Λe stems and in Λe "broken" T loop are Λe same as Λe sequences in Λe A stem and T stem and loop of tRNA Tyr . Detailed Description of the Invention Oligonucleotides suitable for promoting cleavage of target RNA molecules have been constructed. The oligonucleotides are external guide sequence (EGS) molecules for eukaryotic RNAse P which are designed to specifically bind to and promote RNAse P-mediated cleavage of target RNA molecules and to have enhanced nuclease resistance. These EGS molecules differ in structure and size from previous external guide sequences, and are referred to as Short External Guide Sequence (SEGS). A key distinguishing characteristic is Λat SEGS do not, by Λemselves, form a structure similar to Λe T stem and loop of tRNA. SEGS suitable for use in Λe treatment of hepatitis B viral infections have been constructed. As used herein, "external guide sequence" and "EGS" refer to any oligonucleotide Λat forms an active cleavage site for RNAse P in a target RNA. "Short External Guide Sequence" and "SEGS" refer to Λe short forms of EGS described below. The terms "Short External Guide Sequence" and "SEGS" are intended to refer only to Λe short forms of EGS molecules as described below raΛer Λan "short" EGS molecules in general, Λat is, EGS molecules which are merely "short. " To emphasize this distinction, "Short External Guide Sequence" is capitalized herein. Where reference is made herein to external guide sequences it is intended Λat SEGS are encompassed. Previous EGS molecules were designed to form a structure similar to at least Λe T stem and loop of tRNA, with a 3' tail and 5' tail which hybridize to a target RNA molecule to form structures similar to the A stem and D stem of tRNA. It has been discovered Λat the structures similar to Λe T loop and D stem are unnecessary for cleavage of a target RNA/EGS structure. In Λe disclosed Short External Guide Sequence molecules, the SEGS and target RNA molecule togeΛer form structures similar to Λe A stem and T stem of tRNA.. Unlike previous EGS molecules, a SEGS does not form a T loop and does not, by itself, form a structure similar to a T stem. Instead, Λe target RNA molecule hybridizes to Λe SEGS to form half of a structure similar to Λe T stem of tRNA. An example of a SEGS hybridized to its target RNA molecule is shown in Figure 1. SEGS are distinguished from previous EGS molecules in Λat 1) there is no intact T loop, 2) the SEGS and target RNA do not form a structure similar to the D stem of tRNA, and 3) the target RNA, in combination with tae SEGS, forms half of a structure similar to Λe T stem of tRNA. SEGS have several advantages over previous EGS molecules. 1) They are easier to synΛesize and purify SEGS, and Λey will cost less, due to Λeir shorter lengΛ, 2) Λe use of Λe T stem for target recognition will impart more specificity to Λe EGS since Λe short D stems used for target recognition in previous EGS molecules provide less target-specific sequence in Λe EGS, Λereby decreasing Λe specificity of cleavage, and 3) a SEGS will be taken up by Λe cell more readily. I. Design and Synthesis of SEGS Molecules. SEGS molecules are synthetic oligonucleotides that bind to a target substrate to form a secondary and tertiary structure resembling the natural cleavage site of precursor tRNA for eukaryotic RNAse P. The ability of SEGS molecules to target and promote RNAse P activity is readily determined using an in vitro activity assay for cleavage by RNAse P of a target RNA sequence, as described in more detail below. In Λe case of SEGS molecules wiΛ modified nucleotides or nucleotide linkages, a stability assay allows determination of Λe nuclease resistance of various types of modification. The activity assay permits comparison of Λe efficiency of RNAse P-mediated cleavage promoted by SEGS molecules wiΛ different modifications. TogeΛer, Λe assays are used to optimize and balance stability and cleavage efficiency of modified SEGS molecules. Exemplary SEGS molecules have been constructed which are suitable for use in the treatment of viral disease. The specific target is tae hepatitis B virus, more particularly, Λe hepatitis B surface antigen (HBsAg) encoding RNA. Since HBsAg plays, an essential role in viral suprastructure and infection, SEGS-based Λerapeutics can be used to down-regulate hepatitis Λrough cleavage of HBsAg mRNA. Preferred targeted sites wiΛin hepatitis B RNA, or oΛer target RNAs, are regions of conserved sequence which appear in all forms of Λe target RNA and which have a UNR motif as described below. Five such preferred sites have been identified in Λe HBsAg encoding region of hepatitis B RNA and are targeted by SEGS molecules having nucleotide base sequences shown in SEQ ID NO. 6, SEQ ID NO. 8, SEQ ID NO. 10, SEQ ID NO. 12, and SEQ ID NO. 14. A. Design of SEGS Molecules SEGS molecules can be designed by adapting a portion of Λe basic structure of a pre-tRNA molecule to form a substrate recognition sequence. This recognition sequence is complementary to regions of a targeted sequence in a target RNA molecule. In SEGS, Λe recognition sequence is composed of two recognition arms, referred to as Λe A recognition arm and Λe T recognition arm, which, in combination wiΛ regions of Λe targeted sequence in Λe target RNA, form structures similar to Λe A stem and T stem, respectively, of a tRNA molecule. The T recognition arm is located 5' of and adjacent to Λe A recognition arm. The sequence of Λe recognition arms are chosen to be specifically complementary to two regions of the targeted sequence in Λe target RNA, referred to as Λe first target region and Λe second target region. The first target region encompasses, or is adjacent to and 3' of, Λe site where RNAse P-mediated cleavage occurs. The sequences of Λe recognition arms are chosen such Λat Λe first and second target regions in Λe target RNA are separated by a short unpaired region, referred to as the bulge region. Formation of Λis structure is Λe only essential requirement for defining Λe nucleotide sequence of a SEGS. However, it is preferred Λat Λe sequences of Λe recognition arms are also chosen such Λat a UNR motif is present in Λe target RNA molecule adjacent to and 3' of Λe second target region. The UNR motif can be immediately adjacent to the second target region, or it may be separated from Λe second target region by one or a few spacer nucleotides. It is preferred Λat Λe UNR motif is separated from the second target region by from zero to ten spacer nucleotides, more preferred Λat Λe UNR motif is separated from Λe second target region by from zero to three spacer nucleotides, and most preferred that Λe UNR motif is separated from Λe second target region by one spacer nucleotide. The UNR motif has a nucleotide sequence of UNR where N represents any nucleotide, R represents any purine nucleotide, and U represents a uridine nucleotide. The region of the targeted sequence in the target RNA molecule that makes up the UNR motif, or corresponding sequence, and spacer nucleotides is referred to as Λe turn region. The turn region, if present, is immediately adjacent to and 3' of Λe second target region. WiΛout wishing to be limited by any particular Λeory, it is believed Λat Λe potential of Λe turn region of Λe targeted sequence in a target RNA to form a uridine turn structure (see Quigley and Rich, Science 194:796-806 (1976), and Junker and Pardi, RNA 1:219-222 (1995)) aids in promoting RNAse P-mediated cleavage of Λe target RNA. According to Λe relationships described above, Λe targeted sequence in Λe target RNA is composed of, from 5' to 3', Λe first target region, Λe bulge region, and Λe second target region, where the A recognition arm of the SEGS is complementary to Λe first target region and Λe T recognition arm of Λe SEGS is complementary to Λe second target region. It is preferred that a turn region, having a UNR motif, is also present in Λe targeted sequence 3' of Λe second target region. An example of Λese regions and relationships are shown in Figure 1. The recognition arms can be any lengΛ Λat results in a functional SEGS molecule. It is preferred Λat Λe A recogmtion arm and T recognition arm togeΛer total from 12 to 16 nucleotides. It is most preferred Λat Λe A recognition arm and T recognition arm togeΛer total 12 or 13 nucleotides. In general, it is preferred that Λe A recognition arm be from seven to nine nucleotides long, and Λat the T recognition arm be from five to seven nucleotides long. It is most preferred Λat Λe A recognition arm be seven or eight nucleotides long and Λe T recognition arm be five or six nucleotides long. In general, Λe recognition arms can have any nucleotide sequence. As discussed below, Λe choice of sequence is preferably based on Λe sequence of targeted sequence in a target RNA of interest. It is preferred Λat Λe nucleotide at Λe 3' end of Λe A recognition arm is a cytidine or guanidine nucleotide. It is most preferred Λat Λe nucleotide at Λe 3' end of Λe A recognition arm is a cytidine nucleotide. The bulge region can be any lengΛ Λat results in a functional SEGS molecule. It is preferred Λat Λe bulge region be from 1 to 30 nucleotides long. It is more preferred Λat Λe bulge region be from five to fifteen nucleotides long. It is most preferred Λat Λe bulge region be nine nucleotides long. The turn region, if present, can have any sequence that includes Λe consensus formula UNR Λat results in a functional SEGS molecule. The nucleotide sequences of Λe turn region are denoted herein using standard nucleotide base symbols. For reference, N represents any nucleotide, R represents any purine nucleotide, Y represents any pyrimide nucleotide, A represents an adenine nucleotide, C represents a cytosine nucleotide, G represents a guanine nucleotide, T represents a Λymine nucleotide, and U represents a uracil nucleotide. It is preferred Λat Λe turn region has a sequence of NUNR. It is more preferred Λat Λe turn region has a sequence of NUCR or UUNR. It is most preferred that Λe turn region has a sequence of UUCR. It is preferred Λat the turn region of a targeted sequence in a target RNA comprise a nucleotide sequence encompassed by Λe formula NNNR. It is more preferred Λat Λe turn region of a targeted sequence in a target RNA comprise a nucleotide sequence encompassed by at least one of Λe formulas NNYR, YNNR, or NYNR. It is still more preferred Λat the turn region of a targeted sequence in a target RNA comprise a nucleotide sequence encompassed by at least one of Λe formulas YNYR, NYYR, or YYNR. It is still more preferred Λat the turn region of a targeted sequence in a target RNA comprise a nucleotide sequence encompassed by at least one of the formulas YYYR, YUNR, or NUYR. It is still more preferred Λat Λe turn region of a targeted sequence in a target RNA comprise a nucleotide sequence encompassed by at least one of Λe formulas UYYR or YYCR, or at least one of Λe formulas YUYR, UUNR, or NUCR. It is still more preferred that Λe turn region of a targeted sequence in a target RNA comprise a nucleotide sequence encompassed by the formula UYCR, or at least one of Λe formulas UUYR orYUCR. It is most preferred Λat Λe turn region of a targeted sequence in a target RNA comprise a nucleotide sequence encompassed by Λe formula UUCR. Where Λe turn region of a targeted sequence in a target RNA comprises a nucleotide sequence encompassed by Λe formula NNNY, it is preferred Λat Λe turn region comprise a nucleotide sequence encompassed by the formula YNNY. It is more preferred Λat the turn region of a targeted sequence in a target RNA comprise a nucleotide sequence encompassed by at least one of Λe formulas YNYY or YYNY. It is still more preferred Λat Λe turn region of a targeted sequence in a target RNA comprise a nucleotide sequence encompassed by Λe formula YYYY. It is still more preferred Λat Λe turn region of a targeted sequence in a target RNA comprise a nucleotide sequence encompassed by Λe formula YUYY or Λe formula UYCY. It is still more preferred Λat Λe turn region of a targeted sequence in a target RNA comprise a nucleotide sequence encompassed by at least one of Λe formulas UUYY or YUCY. It is most preferred Λat Λe turn region of a targeted sequence in a target RNA comprise a nucleotide sequence encompassed by Λe formula UUCY. Functional SEGS molecules require only Λat Λey form, in combination wiΛ a target RNA, a structure corresponding to Λe A stem and T stem of precursor tRNA such Λat an unpaired region is present in Λe target RNA between Λe structures corresponding to Λe A stem and T stem of tRNA. No structure corresponding to Λe T loop of a tRNA is required. Thus, a functional SEGS molecule requires only a nucleotide sequence complementary to two regions of a target RNA molecule, where Λe regions of Λe target RNA molecule are separated by a region, Λe bulge region, that is not complementary to the SEGS. It is preferred Λat a turn region containing a UNR motif, or anoΛer preferred turn region nucleotide sequence as described above, is also present in Λe target RNA adjacent to and 3 ' of Λe structure corresponding to Λe T stem of tRNA. SEGS can be designed to target any sequence in any target RNA of interest. However, SEGS are preferably designed by searching Λe nucleotide sequence of a target RNA of interest for Λe location of UNR motifs, or anoΛer preferred turn region nucleotide sequence as described above. For more preferred SEGS, Λe search can be limited to Λe preferred sequences of turn regions as described above. Once a desired turn sequence is identified, Λe sequence of Λe T recognition arm of Λe SEGS is chosen to be complementary to nucleotides in Λe target RNA adjacent to and 5' of Λe tern region sequence, separated by one or a few spacer nucleotides, if desired. These nucleotides in Λe target RNA represent Λe second target region. The sequence of Λe A recognition arm of Λe SEGS is chosen to be complementary to nucleotides in Λe target RNA 5' of Λe second target region, separated by an unpaired region. The unpaired region is Λe bulge region in Λe targeted sequence. Design of a SEGS can be illustrated wiΛ an example. A portion of Λe nucleotide sequence of hepatitis B virus which contains a UNR motif is: CUGGAUGUGUCUGCGGCGUUUUAUCAUCUUCCUCUUCAUCC UGCUGCUAU (SEQ ID NO. 7; UNR motif in bold). Choosing a T recognition arm length of five nucleotides, a bulge region lengΛ of nine nucleotides, an A recognition arm lengΛ of eight nucleotides, and a single spacer nucleotide in Λe turn region, Λe sequence for Λe SEGS is Λe complement of Λe five nucleotides adjacent to and 5' of Λe turn region, which includes a spacer nucleotide (U) 5' of Λe UNR motif, followed by Λe complement of Λe seven nucleotides starting at Λe fifteenΛ nucleotide 5' of Λe turn region. This SEGS (HBV B) will have a sequence of GAGGAAACGCCGC (SEQ ID NO. 6; T recognition arm in bold). The structure of the complex of SEGS HBV B and HBV RNA is shown in Figure 7. OΛer examples also involving HBV are shown in Figures 8, 9, 10, and 11. SEGS molecules may also contain additional nucleotide sequences at eiΛer or boΛ of Λe 3' end. of Λe A recognition arm and Λe 5' end of the T recogmtion arm. Such nucleotide regions are distinguished from Λe recognition sequence of Λe SEGS in Λat Λey are not complementary to Λe targeted sequence of Λe target RNA. Such sequences are not considered to be a part of Λe recognition sequence of Λe SEGS. An example of such an additional nucleotide sequence, at the 5' end of Λe T recognition arm, is shown in Figure 2. SEGS molecules can be readily screened for Λe ability to promote cleavage, by RNAse P, of target RNA using Λe assay described in Yuan et al., Proc. Natl. Acad. Sci., USA, 89:8006-8010 (1992) or Λe assay described below. A SEGS and Λe catalytic RNA subunit of an RNAse P can be coupled to form a single oligonucleotide molecule possessing boΛ Λe targeting function of Λe SEGS and cleavage function of RNAse P catalytic RNA. Such a combination, in a single oligonucleotide molecule, is referred to as an RNAse P internal guide sequence (RIGS). A RIGS can be used to cleave a target RNA molecule in Λe same manner as SEGS. RIGSs can be formed by linking a guide sequence to an RNAse P catalytic sequence by any suitable means. For example, an SEGS and RNAse P catalytic RNA can be prepared as separate molecules which are then covalently coupled in vitro. Alternatively, a complete RIGS can be synΛesized as a single molecule, eiΛer by chemical synΛesis, or by in vitro or in vivo transcription of a DNA molecule encoding linked SEGS and RNAse P catalytic sequence. The linkage between Λe SEGS and RNAse P domains of an RIGS can have any form that allows Λe domains to cleave a target RNA. For example, Λe two domains could be joined by an oligonucleotide linker. Preferably, Λe linker will be composed of ordinary nucleotides joined by phosphodiester bonds. The SEGS and RNAse P catalytic sequence components can be joined in eiΛer order, with Λe RNAse P catalytic sequence linked to eiΛer the 3' end or 5' end of Λe SEGS component. MeΛods for Λe construction and use of RIGS are described in PCT application WO 95/24489 by Yale University. The SEGS molecules can also be regulatable. A regulatable SEGS molecule is a SEGS sequence, as described above, linked to a ligand-binding sequence, placing Λe activity of Λe SEGS molecule under Λe control of Λat ligand and requiring Λe presence of Λe ligand for activation or inactivation. RNA molecules are constructed in which one portion is capable of binding a ligand and Λe oΛer portion is a SEGS sequence. After Λe selection of molecules which bind Λe ligand, a second selection process occurs in which Λe ligand-binding molecules are assayed for Λeir catalytic function in Λe presence and absence of Λe ligand or "co-drug. " In this manner regulatable SEGS molecules are selected for use in cleaving a target RNA in Λe presence of a ligand, or in cleaving a target RNA in Λe absence of a ligand. This meΛod and regulatable SEGS molecules are useful in cleaving a target RNA molecule in a controlled fashion. It is particularly useful when Λe target RNA molecule is present in a cell where it is not desirable to kill Λe host cell by complete inactivation of Λese RNA molecules. The formation, selection and use of regulatable EGS molecules is fully described in PCT applications WO 94/13791 and WO 94/13833. The same meΛods can be used to form select and use regulatable SEGS molecules. MeΛods to produce or synΛesize SEGS molecules, and DNA sequences encoding SEGS molecules having a known sequence, can be routinely synΛesized using automated nucleic acid synΛesis, for example, using Λe cyanoetayl phosphoramidite meΛod on a DNA model 392 synΛesizer by Applied Biosystems, Inc. (Foster City, CA) or a Pharmacia Oligo Pilot (Pharmacia, Piscataway, NJ). OΛer meΛods for synΛesizing nucleic acid molecules are also available (see, for example, Ikuta et al., Ann. Rev. Biochem. 53:323-356 (1984) (phosphotriester and phosphite-triester meΛods); Narang et al , Methods Enzymol. 65:610-620 (1980) (phosphotriester meΛod). Alternatively, SEGS molecules can be synΛesized by transcribing DNA templates, for example, wiΛ T7 RNA polymerase (Milligan et al, Nucl Acids Res. 15:8783 (1987)). SEGS molecules can also be synΛesized in cells by placing a vector that encodes and expresses Λe SEGS in the cells. B. Activity of SEGS Molecules An in vitro cleavage assay which measures Λe percentage of substrate RNA remaining after incubation with various amounts of a SEGS, in Λe presence of a non-limiting amount of RNAse P, is used as an indicator of Λe potential activity of Λe SEGS/RNAse P complex. SEGS/RNAse P complexes Λat exhibit the highest in vitro activity are selected for further testing. The percentage of RNA remaining can be plotted as a function of Λe SEGS concentration. The catalytic efficiency of an SEGS/RNAse P can be expressed as k ^ /K π , (where I ^ is Λe rate constant of cleavage and K^ is Λe Michaelis constant), Λe second order rate constant for Λe reaction of a free SEGS and substrate RNA molecule. Following Λe meΛods of Heidenreich and Eckstein (J. Biol. Chem. , 267: 1904-1909 (1992)), Y^ is determined using Λe formula -In F/t = (k^/K^C] where F is Λe fraction of substrate left, t is Λe reaction time, and [C] is Λe SEGS concentration. Preferred SEGS constructs are Λose which bind to and promote Λe preferential RNAse P cleavage of Λe hepatitis substrate RNA. Preferred constructs can be selected using Λe ribozyme cleavage assay, as described in Example 1 , and determining which constructs are Λe most efficient at mediating specific RNAse P cleavage of hepatitis substrate RNA sequence as determined by Λe value of k^/K π , , as described above. Intracellular activity of SEGS can be tested using cells expressing Λe target RNA of interest. For example, SEGS molecules targeted to various regions of HBV RNA having Λe NUNR motif as described above can be tested in cells expressing HBV RNA. For Λis, SEGS can be tested in HepG2.2.15 cells, which constitutively express HBV RNA and fully assembled HBV particles (Sells et al , Proc. Natl. Acad. Sci. USA, 84: 1005- 1009 (1987)), for inhibition of viral replication. The assays can be preformed generally as described by Korba and Gerin (Antiviral Res. 19:55- 70 (1992)). The SEGS molecules can be delivered to Λe cells as a complex wiΛ heme lipid particles, specifically l,2-dioleoyloxy-3- (trimeΛylammonium)propane (DOTAP) and dioleoyl phosphatidyl eΛanolamine (DOPE) conjugated with heme (referred to as DDH), for ten days and Λe DNA genome of HBV particles secreted into the media can be assayed using dot-blot assays. Heme lipid particles can be prepared generally as follows. Heme (as Fe protoporphyrin IX chloride, hemin) is dissolved in eΛanol containing 8.3 mM NaOH, and insoluble material is pelleted at 14 krpm for 10 minutes. To allow effective conjugation using carbodiimide, Λe pH of Λe heme solution is-reduced by Λe addition of small volumes of HC1 wiΛout precipitation of heme. In a typical reaction, 200 mg hemin is added to 10 ml eΛanol containing 8.3 mM NaOH. HC1 is added to Λe supernatant heme solution to bring Λe pH down to 1.7, Λe heme solution (containing approximately 1.6 mg heme), 760 μl (10 μmol) DOPE (10 mg/ml) and 500 μl DCC (10 mg/ml) is added and Λe conjugation is allowed to proceed overnight at room temperature in Λe dark. Ten micromoles DOTAP in chloroform are added to Λe heme-conjugated DOPE in a sterile glass test tube and Λe lipids are dried to a Λin film, under vacuum in a vortex desiccator at 50 °C for 20 minutes. One milliliter sterile 150 mM NaCl is added to Λe lipid film and Λe emulsion was sonicated for 30 minutes in a Bransonic 1210 baΛ sonicator, operated at 47 kHz at 20 °C, to give a turbid solution. The lipid particles are extruded Λrough a polycarbonate membrane using a Lipex Extruder (Lipex Biomembranes, Vancouver, Canada). The SEGS/lipid compositions are prepared by bringing solutions containing Λe SEGS molecules to 150 mM NaCl, and DDH lipid particles (in 150 mM NaCl) are added Λe SEGS solution to a final concentration of 0.2 mg/ml. After incubating for 15 minutes at room temperature, culture medium is added and Λe SEGS/lipid mixture is diluted to obtain SEGS compositions wiΛ Λe desired final concentration of SEGS. An equivalent volume of 150 mM NaCl is used as a control. Confluent cultures of HepG2.2.15 cells are maintained on 96-well flat-bottomed culture plates.. Duplicate plates are used for each SEGS treatment. A total of three cultures on each plate are treated wiΛ each of Λe diluted SEGS compositions. Cultures are treated wiΛ 10 consecutive daily doses of Λe SEGS compositions. Medium is changed daily wiΛ fresh SEGS compositions. The effect of Λese treatments is monitored by measuring extracellular HBV DNA levels. The anti-viral activities of Λese SEGSs can be calculated as an EC 50 . The EC 50 is Λe concentration of a compound at which Λere is a 50% reduction in Λe amount of HBV produced relative to cells treated wiΛ Λe control composition. For comparison, Λe anti-viral effect of 2'-3'-ddC, a known potent anti-HBV nucleoside analog, can be measured in the same assays. A phenol red assay measuring Λe viability of cells Λat receive Λe SEGS can be used to determine if there is any toxicity (defined as greater Λan 50% depression of Λe dye uptake levels observed in untreated cells) associated wiΛ Λe administration of the SEGS. π. Nuclease Resistant SEGS molecules A. Types of Modifications AlΛough unmodified oligoribonucleotides can function as effective SEGS in a nuclease-free environment, Λe short half-life in serum and inside cells reduces Λeir effectiveness as Λerapeutics. Chemical modifications can be made which greatly enhance Λe nuclease resistance of SEGS wiΛout compromising its biological function of promoting RNase P-mediated cleavage of target RNA. In general, such modifications can be made at Λe 2' position of Λe nucleotides in a SEGS, Λe 3' and 5' ends of a SEGS, and in Λe phosphate linkages between Λe nucleotides in a SEGS. For example, one or more of Λe bases of an SEGS construct can be replaced by 2' meΛoxy ribonucleotides, phosphorothioate deoxyribonucleotides, or phosphoroΛioate ribonucleotides using available nucleic acid synΛesis meΛods. Modified nucleotides and oligonucleotides, and meΛods for Λeir synΛesis, are known. Some of Λese are described in Offensperger et. al , EMBO J. , 12: 1257-1262 (1993); WO 93/01286 by Rosenberg et al ; Agrawal et al , Proc. Natl Acad. Sci. USA, 85:7079-7083 (1988); Sarin et al , Proc. Natl Acad. Sci. USA, 85:7448-7794 (1989); Shaw et al , Nucleic Acids Res, 19:747-750 (1991); Orson et al , Nucl. Acids Res. , 19:3435-3441 (1991); Paolella et al, EMBO J., 11: 1913-1919 (1992); Pieken, et al , Science, 253:314-317 (1991); Heidenreich and Eckstain, J. Biol. Chem, 267: 1904- 1909 (1992); WO 91/17093 by Hybridon, Inc.; EP 0339842 by Ajinomoto Co., Inc. ; WO 95/23225 by Ribozyme Pharmaceuticals, Inc. ; WO 94/15619 by Johns Hopkins University; and U.S. Patent 5,334,711 to Sproat et al. In describing substituents used to modify nucleotides, oligonucleotides and SEGS, alkyl or alkyl group refers to a saturated aliphatic hydrocarbon, including straight chain, branch chain, and cyclic alkyl groups. For Λis use it is preferred that such alkyl groups have 1 to 12 carbons. It is more preferred Λat such alkyl groups have 1 to 6 carbons. It is still more preferred Λat such alkyl groups have 1 to 2 carbons. It is most preferred that such alkyl groups have 1 carbon. These alkyl groups can also include one or more hydroxyl groups, one or more amino groups, or boΛ. Such hydroxyl and amino groups can be coupled to any carbon atom in Λe alkyl group. As used herein, Λe term hydroxy alkyl is used to refer to an alkyl group including one or more hydroxyl groups, Λe term amino alkyl is used to refer to an alkyl group including one or more amino groups, and hydroxylamino alkyl is used to refer to an alkyl group including one or more hydroxyl groups and one or more amino groups. As used herein, allyl or allyl group refers to an usaturated aliphatic hydrocarbon, including straight chain, branch chain, and cyclic allyl groups. For this use it is preferred Λat such allyl groups have 1 to 12 carbons. It is more preferred Λat such allyl groups have 1 to 6 carbons. It is still more preferred Λat such allyl groups have 2 to 3 carbons. It is most preferred Λat such allyl groups have 3 carbons. OΛer substituents can also be used to modify tae nucleotides, oligonucleotides and SEGS described herein, such as aryl, alkaryl, and arylalkyl, where aryl refers to a benzyl group, alkaryl refers to an alkyl group substituted wiΛ an aryl group, and arylalkyl refers to an aryl group substituted wiΛ an alkyl group. Use herein of Λe term modification in reference to nucleotides, oligonucleotides and SEGS is intended to refer to chemical differences of a nucleotide or oligonucleotide relative to conventional nucleotides and oligonucleotides. Use of Λe term modification herein is not intended to limit the manner in which the modified nucleotides, oligonucleotides or SEGS are produced. Similarly, references to replacing a chemical group on a nucleotide, oligonucleotide or SEGS is intended to refer to chemical differences of a nucleotide or oligonucleotide relative to conventional nucleotides and oligonucleotides, and is not intended to limit Λe manner in which Λe nucleotides, oligonucleotides or SEGS are produced. 1. Modifications at the 3' and 5' ends. It is well documented in Λe current literature Λat degradation of oligonucleotide analogues is mainly attributable to 3'-exonucleases. Several studies have also demonstrated Λat various 3 '-modifications can greatly decrease Λe nuclease susceptibility of Λese analogues. Thus, anoΛer meΛod to reduce susceptibility to 3' exonucleases is introduction of a free amine to a 3' terminal hydroxyl group of Λe SEGS molecule (see, for example, Orson et al. , Nucl. Acids Res. , 19:3435-3441 (1991)). AnoΛer useful 3' terminal modification is to couple a Λymine nucleotide end of an SEGS wiΛ a 3' to 3' linkage. Such a structure is referred to herein as 3'-3'-thymine nucleotide or T(3'-3'). Preferred 3' modifications are those where Λe 3' hydroxyl of Λe Short External Guide Sequence is replaced wiΛ a chemical group such as -H, -O-R 1 , -NH 2 , -NH-R 1 , -N-R' 2 , F, and -3 '-nucleotide, where each R 1 is independently alkyl, hydroxy alkyl, amino alkyl, hydroxylamino alkyl, allyl, -PR 2 (O)-R 2 , or -PR 2 (S)-R 2 , where each R 2 is independently O, S, F, alkyl, hydroxy alkyl, amino alkyl, hydroxylamino alkyl, allyl, O-R 3 , or S-R 3 , and where each R 3 is independently alkyl, hydroxy alkyl, amino alkyl, hydroxylamino alkyl, or allyl. More preferred 3' modifications are Λose where Λe 3' hydroxyl of Λe Short External Guide Sequence is replaced wiΛ a chemical group such as -H, -O-CH 3 , -NH 2 , -NH-CH 3 , -N-(CH 3 ) 2 , F, -3'-Λymine nucleotide, -OPO(O)-CH 3 , -OPO(S)-CH 3 , -OPO(O)OCH 2 CH(OH)-CH 2 NH 2 , and -OPO(S)OCH 2 CH(OH)-CH 2 NH 2 . The most preferred 3' modifications are those where Λe 3' hydroxyl of Λe Short External Guide Sequence is replaced wiΛ -3'-Λymine nucleotide, -OPO(O)OCH 2 CH(OH)-CH 2 NH 2 , or -OPO(S)OCH 2 CH(OH)-CH 2 NH 2 . As used herein, Λe 3' hydroxyl of a SEGS refers to Λe hydroxyl group that would normally be present on Λe 3' carbon of the ribose residue in Λe 3' terminal nucleotide of Λe SEGS. As used herein, Λe 3' carbon of a SEGS refers to Λe 3' carbon of Λe ribose residue in Λe 3' terminal nucleotide of Λe SEGS. AlΛough it is preferred Λat Λe 5' end of SEGS have a hydroxyl or phosphate group, Λe 5' end can be modified to increase resistance of Λe SEGS to nucleases. Preferred 5' modifications are Λose where Λe 5' hydroxyl of Λe Short External Guide Sequence is replaced wiΛ a chemical group such as -H, -O-R 4 , -NH 2 , -NH-R 4 , -N-R 4 2 , and F, where each R 4 is independently alkyl, hydroxy alkyl, amino alkyl, hydroxylamino alkyl, allyl, -PR 5 (O)-R 5 , or -PR 5 (S)-R 5 , where each R 5 is independently O, S, F, alkyl, hydroxy alkyl, amino alkyl, hydroxylamino alkyl, allyl, O-R 6 , or S-R 6 , and where each R 6 is independently alkyl, hydroxy alkyl, amino alkyl, hydroxylamino alkyl, or allyl. More preferred 5' modifications are Λose where Λe 5' hydroxyl of Λe Short External Guide Sequence is replaced wiΛ a chemical group such as -H, -O-CH 3 , -NH 2 , -NH-CH 3 , -N-(CH 3 ) 2 , F, -OPO(O)-CH 3 , -OPO(S)-CH 3 , -OPO(O)OCH 2 CH(OH)-CH 2 NH 2 , and -OPO(S)OCH 2 CH(OH)-CH 2 NH 2 . The most preferred 5' modifications are Λose where Λe 5' hydroxyl of Λe Short External Guide Sequence is replaced wiΛ -OPO(O)OCH 2 CH(OH)-CH 2 NH 2 , or -OPO(S)OCH 2 CH(OH)-CH 2 NH 2 . As used herein, Λe 5' hydroxyl of a SEGS refers to Λe hydroxyl Λat would normally be present on the 5' carbon of the ribose residue in Λe 5' terminal nucleotide of Λe SEGS to which a phosphate group would normally be attached. As used herein, Λe 5' carbon of a SEGS refers to Λe 5' carbon of Λe ribose residue in Λe 5' terminal nucleotide of Λe SEGS. AnoΛer useful modification is covalent attachment of an intercalating agent, such as an acridine derivative, to Λe 5' terminal phosphate (for example, using a pentameΛylene bridge) (see, for example, Maher et al , Science, 245:725- 730 (1989); Grigoriev et al , J. Biol. Chem. , 267:3389-3395 (1992)). WO 95/23225 describes chemical modifications for increasing Λe stability of ribozymes, such as Λe introduction of an alkyl group at Λe 5' carbon of a nucleoside or nucleotide sugar. Such modifications can also be used in SEGS molecules. 2. Modifications at the 2' position of nucleotides. AnoΛer class of chemical modifications expected to be useful is modification of Λe 2' OH group of a nucleotide 's ribose moiety, which has been shown to be critical for Λe activity of Λe various intracellular and extracellular nucleases. Typical 2' modifications are Λe synΛesis of 2'-O-MeΛyl oligonucleotides (Paolella et al, EMBO J., 11: 1913-1919, 1992) and 2'- fluoro and 2'-amino- oligonucleotides (Pieken, et al, Science, 253:314-317 (1991); Heidenreich and Eckstain, /. Biol Chem, 267: 1904-1909 (1992)). SEGS molecules can also contain deoxyribonucleotides. Such substitutions improve nuclease resistance by eliminating Λe critical 2' OH group. WO 95/23225 describes 2 '-deoxy-2' -alky .nucleotides which may be present to enhance Λe stability of oligonucleotides. Preferred 2' modifications are Λose where Λe 2' hydroxyl of a nucleotide is replaced wiΛ a chemical group such as -H, -O-R 7 , -NH 2 , -NH- R 7 , -N-R 7 2 , F, and -2 '-nucleotide, where each R 7 is independently alkyl, hydroxy alkyl, amino alkyl, hydroxylamino alkyl, allyl, -PR 8 (O)-R 8 , or -PR 8 (S)-R 8 , where each R 8 is independently O, S, F, alkyl, hydroxy alkyl, amino alkyl, hydroxylamino alkyl, allyl, O-R 9 , or S-R 9 , and where each R 9 is independently alkyl, hydroxy alkyl, amino alkyl, hydroxylamino alkyl, or allyl. More preferred 2' modifications are Λose where Λe 2' hydroxyl of a nucleotide is replaced wiΛ a chemical group such as -H, -O-CH 3 , -NH 2 , - NH-CH 3 , -N-(CH 3 ) 2 , F, -OCH 2 -CH=CH 2 , -OPO(O)-CH 3 , and -OPO(S)- CH 3 . The most preferred 2' modification is where Λe 2' hydroxyl of a nucleotide is replaced wiΛ -O-CH 3 . 3. Modifications to the phosphate linkages. Modification to Λe phosphate groups linking nucleotides in a SEGS can also be used to enhance Λe resistance of Λe SEGS to nucleases. Typical modification for this purpose include replacing one or boΛ of the free oxygen atoms sulfur or a halogen. The free oxygen atoms, or a sulfur atom, if present, can also be linked to chemical groups such as alkyl, hydroxy alkyl, amino alkyl, hydroxylamino alkyl, or allyl. Examples of such substitutions, such as Λe use of 3' and/or 5' dihalophosphonate substituted nucleotides (for example, 3' and/or 5'-CF 2 -phosphonate substituted nucleotides), are described in WO 95/23225. Preferred modified phosphate linking groups for use in SEGS include -OPR 10 (O)O-, -OPR'°(S)O-, and -OPO(S)O-, where R 10 is alkyl, hydroxy alkyl, amino alkyl, hydroxylamino alkyl, allyl, -O-R 11 , -NH 2 , -NH- R 11 , -N-R π 2 , or F, and where each R 11 is independently alkyl, hydroxy alkyl, amino alkyl, hydroxylamino alkyl, or allyl. More preferred modified phosphate linking groups for use in SEGS include -OPR 12 (O)O-, -OPR ,2 (S)O- , and -OPO(S)O-, where R 12 is -CH 3 , -O-CH 3 , -OCH 2 -CH=CH 2 , -NH 2 , -NH- CH 3 , -N-(CH 3 ) 2 , or F. The most preferred modified phosphate linking group for use in SEGS is -OPO(S)O-, which is commonly referred to as a phosphorothioate . AnoΛer useful modification is meΛylation of cytosine bases Λat may be present in Λe sequence. The stability of SEGS/target RNA hybrids can be increased by using modified nucleotides Λat result in oligonucleotides wiΛ stronger base pairing to Λe target RNA. For example, C-5 propynyl pyrimide nucleotides increase hydrogen bonding between nucleic acids (Froehler et al, Tetrahedron Letters 33:5307-5310 (1992)). The extent to which modifications affect Λe efficiency wiΛ which a modified SEGS molecule promotes ribozyme-mediated cleavage of target RNA can readily be determined using Λe cleavage assay described above. B. Chimcric SEGS Molecules The above modifications can be used throughout a SEGS molecule, in limited regions of a SEGS molecule and/or in combinations to result in chimeras of modified SEGS molecules. It is expected Λat all of Λe nucleotides in a SEGS can be chemically modified without significantly reducing its ability to promote RNAse P-mediated cleavage of a target RNA. For example, it has been discovered that 2'-O-meΛyl modified nucleotides can be used Λroughout a SEGS wiΛout a significant loss of RNAse P targeting activity. The extent to which modifications affect Λe efficiency wiΛ which Λe modified SEGS molecule promotes RNAse P-mediated cleavage of a target RNA can readily be determined using Λe cleavage assay described above. Chemically modified SEGS molecules can be classified according to the level of ribozyme cleavage activity promoted by Λe modified SEGS when compared wiΛ Λe ribozyme cleavage activity promoted by an unmodified SEGS, Λat is, an SEGS molecule having Λe same nucleotide sequence as Λe modified SEGS but which is comprised of unmodified ribonucleotides, unmodified phosphodiester linkages, and unmodified 3' and 5' ends. This comparison provides Λe relative ribozyme cleavage activity promoted by Λe modified SEGS molecule, which is preferably expressed as a percentage of Λe ribozyme cleavage activity promoted by the unmodified SEGS molecule. Modified SEGS molecules can be divided into classes based on Λese activity levels. In Λis way, modified SEGS molecules can be divided, for example, into four classes: (1) modified SEGS molecules promoting greater Λan 70% of Λe ribozyme cleavage activity promoted by an unmodified SEGS, (2) modified SEGS molecules promoting from 50% to 70% of Λe ribozyme cleavage activity promoted by an unmodified SEGS, (3) modified SEGS molecules promoting from 25% to 50% of the ribozyme cleavage activity promoted by an unmodified SEGS, and (4) modified SEGS molecules promoting less Λan 25 % of the ribozyme cleavage activity promoted by an unmodified SEGS. Preferred modified SEGS molecules promote at least 25% of Λe ribozyme cleavage activity promoted by an unmodified SEGS. More preferred SEGS molecules promote at least 50% of Λe ribozyme cleavage activity promoted by an unmodified SEGS. The most preferred SEGS molecules promote at least 70% of Λe ribozyme cleavage activity promoted by an unmodified SEGS. III. Cloning and Expression Vectors Preferred vectors for introducing SEGS molecules into mammalian cells include viral vectors, such as the retroviruses, which introduce DNA which encodes an SEGS molecule directly into Λe nucleus where Λe DNA is then transcribed to produce Λe encoded SEGS molecule. Examples of meΛods for using retroviral vectors for gene Λerapy are described in U.S. Patent Nos. 4,868,116 and 4,980,286; PCT applications WO 90/02806 and WO 89/07136; and Mulligan, Science 260:926-932 (1993). Defective retroviral vectors, which incorporate Λeir own RNA sequence in Λe form of DNA into Λe host chromosome, can be engineered to incorporate an SEGS into Λe cells of a host, where copies of Λe SEGS will be made and released into Λe cytoplasm or are retained in Λe nucleus to interact wiΛ Λe target nucleotide sequences of the hepatitis RNA. Bone marrow stem cells and hematopoietic cells are relatively easily removed and replaced from humans, and provide a self-regenerating population of cells for Λe propagation of transferred genes. Such cells can be transfected in vitro or in vivo wiΛ retrovirus-based vectors encoding SEGS molecules. When in vitro transfection of stem cells is performed, once Λe transfected cells begin producing Λe particular SEGS molecules, Λe cells can be added back to Λe patient to establish entire clonal populations of cells Λat are expressing SEGS and are Λerefore resistant to viral infection, transformation, and oΛer disorders. As an example, a vector used to clone and express DNA sequences encoding constructs might include: 1. A cloning site in which to insert a DNA sequence encoding an SEGS molecule to be expressed. 2. A mammalian origin of replication (optional) which allows episomal (non-integrative) replication, such as Λe origin of replication derived from Λe Epstein-Barr virus. 3. An origin of replication functional in bacterial cells for producing required quantities of Λe DNA encoding the SEGS constructs, such as Λe origin of replication derived from the pBR322 plasmid. 4. A promoter, such as one derived from Rous sarcoma virus (RSV), cytomegalovirus (CMV), or Λe promoter of Λe mammalian U6 gene (an RNA polymerase III promoter) which directs transcription in mammalian cells of Λe inserted DNA sequence encoding Λe SEGS construct to be expressed. 5. A mammalian selection marker (optional), such as neomycin or hygromycin resistance, which permits selection of mammalian cells Λat are transfected wiΛ Λe construct. 6. A bacterial antibiotic resistance marker, such as neomycin or ampicillin resistance, which permits Λe selection of bacterial cells Λat are transformed wiΛ Λe plasmid vector. A preferred vector for delivering and expressing SEGS molecules in vivo uses an RNA polymerase III (pol III) promoter for expression. Such promoters can produce transcripts constitutively wiΛout cell type specific expression. Pol III promoters also generate transcripts Λat can be engineered to remain in Λe nucleus of Λe cell, Λe location of many target RNA molecules. It is preferred Λat a complete pol III transcription unit be used, including a pol III promoter, capping signal, and termination sequence. Pol III promoters, and oΛer pol III transcription signals, are present in tRNA genes, 5S RNA genes, small nuclear RNA genes, and small cytoplasmic RNA genes. Preferred pol III promoters for use in SEGS expression vectors are Λe human small nuclear U6 gene promoter and tRNA gene promoters. The use of U6 gene transcription signals to produce short RNA molecules in vivo is described by Noonberg et al, Nucleic Acids Res. 22:2830-2836 (1995), and Λe use of tRNA transcription signals is described by Thompson et al, Nucleic Acids Res., 23:2259-2268 (1995). Many pol III promoters are internal, that is, they are within Λe transcription unit. Thus, Λese pol III transcripts include promoter sequences. To be useful for expression of SEGS molecules, Λese promoter sequences should not interfere wiΛ Λe structure or function of Λe SEGS. Since SEGS molecules are derived from. tRNA molecules, tRNA gene promoter sequences can be easily incorporated into SEGS molecules. The internal promoter of tRNA genes occurs in two parts, an A box and a B box. In tRNA molecules, A box sequences are generally present in Λe D loop and half of Λe D stem of tRNA molecules, and B box sequences are generally present in the T loop and Λe proximal nucleotides in Λe T stem. SEGS molecules lack most of Λese structures. However, boΛ Λe B box and A box sequences can be appended to Λe 5' end of Λe SEGS, after Λe T recognition arm, such Λat Λe proper spacing between Λe A box and B box is maintained. The U6 gene promoter is not internal (Kunkel and Pederson, Nucleic Acids Res. 18:7371-7379 (1989); Kunkel et al, Proc. Natl Acad. Sci. USA 83:8575-8579 (1987); Reddy et al , J. Biol Chem. 262:75-81 (1987)). Suitable pol III promoter systems useful for expression of SEGS molecules are described by Hall et al , Cell 29:3-5 (1982), Nielsen et al, Nucleic Acids Res. 21:3631-3636 (1993), Fowlkes and Shenk, Cell 22:405-413 (1980), Gupta and Reddy, Nucleic Acids Res. 19:2073-2075 (1990), Kickoefer et al, J. Biol Chem. 268:7868-7873 (1993), and Romero and Blackburn, Cell 67:343-353 (1991). The use of pol III promoters for expression of ribozymes is also described in WO 95/23225 by Ribozyme Pharmaceuticals, Inc. IV. Therapy A. Pharmaceutical Compositions SEGS molecules can be used directly in combination wiΛ a pharmaceutically acceptable carrier to form a pharmaceutical composition suited for treating a patient. Alternatively, an SEGS can be delivered via a vector containing a sequence which encodes and expresses Λe SEGS molecule specific for a particular RNA. Direct delivery involves the insertion of pre-synΛesized SEGS molecules into Λe target cells, usually wiΛ Λe help of lipid complexes (liposomes) to facilitate Λe crossing of Λe cell membrane and oΛer molecules, such as antibodies or oΛer small ligands such as heme or anoΛer porphyrin or phΛalocyanin, to maximize targeting. Porphyrins complex wiΛ oligonucleotides, protecting as well as enhancing delivery to cells such as hepatocytes. Because of Λe sensitivity of RNA to degradation, in many instances, directly delivered SEGS molecules may be chemically modified, making Λem nuclease-resistant, as described above. This delivery meΛodology allows a more precise monitoring of the Λerapeutic dose. Vector-mediated delivery involves Λe infection of Λe target cells wiΛ a self-replicating or a non-replicating system, such as a modified viral vector or a plasmid, which produces a large amount of Λe SEGS encoded in a sequence carried on Λe vector. Targeting of Λe cells and Λe mechanism of entry may be provided by Λe virus, or, if a plasmid is being used, meΛods similar to Λe ones described for direct delivery of SEGS molecules can be used. Vector-mediated delivery produces a sustained amount of SEGS molecules. It is substantially cheaper and requires less frequent administration Λan a direct delivery such as intravenous injection of Λe SEGS molecules. The direct delivery meΛod can be used during Λe acute critical stages of infection. Preferably, intravenous or subcutaneous injection is used to deliver SEGS molecules directly. It is essential Λat an effective amount of oligonucleotides be delivered in a form which minimizes degradation of Λe oligonucleotide before it reaches Λe intended target site. Most preferably, Λe pharmaceutical carrier specifically delivers Λe SEGS to affected cells. For example, hepatitis B virus affects liver cells, and Λerefore, a preferred pharmaceutical carrier delivers anti-hepatitis SEGS molecules to liver cells. HBV, a member of a group of small DNA-containing viruses Λat cause persistent non-cytopaΛic infections of Λe liver, is an infectious agent of humans that is found worldwide and which is perpetuated among humans in a large reservoir of chronic carriers. It is estimated that about 6-7% of Λe earth's population is infected (300 million carriers). The prevalence of Λe infection is not uniform throughout Λe world. There is a geographic gradient in distribution of HBV. It is lowest in North America and Western Europe, where Λe virus can be detected in 0.1 to 0.5% of the population, and highest in SouΛeast Asia and sub-Saharan Africa, where Λe frequency of infection may vary from 5 to 20% of Λe population. This skewed distribution parallels that of hepatocellular carcinoma and provides strong epidemiologic evidence for an association between chronic HBV infection and this type of malignancy. Hepatitis B is of great medical importance because it is probably the most common cause of chronic liver disease, including hepatocellular carcinoma in humans. Infected hepatocytes continually secrete viral particles Λat accumulate to high levels in Λe blood. These particles are of two types: (i) noninfectious particles consisting of excess viral coat protein (HBsAg) and containing no nucleic acid (in concentrations of up to 10 13 particles/ml blood), and (ii) infectious, DNA-containing particles (Dane particles) consisting of a 27 nm nucleocapsid core (HBcAg) around which is assembled an envelope containing Λe major viral coat protein, carbohydrate, and lipid, present in lower concentrations (10 9 particles/ml blood). The human hepatitis B virus is a member of Λe Hepadna Viridae family, wiΛ close relatives including woodchuck hepatitis virus (WHV), duck hepatitis virus (DHV), and ground squirrel hepatitis virus (GHV) (Robinson (1990)). Like retroviruses, Λe hepadnavirus utilizes reverse transcription of its 3.2 kb DNA genome (Pugh (1990)). The genome of hepatitis B virus is circular and partially single-stranded, containing an incomplete plus strand. The incomplete plus strand is complexed wiΛ a DNA polymerase in the virion which has been shown to elongate Λe plus strand using Λe complete minus strand as Λe template. These morphological and structural features distinguish hepatitis B viruses from all known classes of DNA-containing viruses. The replication cycle of hepatitis B viruses is also strikingly different from oΛer DNA-containing viruses and suggests a close relationship wiΛ Λe RNA-containing retroviruses. The principal unusual feature is the use of an RNA copy of Λe genome as an intermediate in Λe replication of Λe DNA genome. Infecting DNA genomes are converted to a double-stranded form which serves as a template for transcription of RNA. Multiple RNA transcripts are synthesized from each infecting genome, which either have messenger function or DNA replicative function. The latter, termed "pre- genomes," are precursors of Λe progeny DNA genomes because Λey are assembled into nucleocapsid cores and reverse-transcribed into DNA before coating and export from Λe cell. Thus each mature virion contains a DNA copy of Λe RNA pre-genome and a DNA polymerase. The first DNA to be synΛesized is of minus strand polarity and is initiated at a unique site on Λe viral genetic map. Very small nascent DNA minus strands (less Λan 30 nucleotides) are covalently linked to a protein, and are likely to act as primer for minus strand DNA synΛesis. GrowΛ of Λe minus strand DNA is accompanied by a coordinate degradation of Λe pre-genome so Λat Λe product is a full-length single-stranded DNA, raΛer Λan an RNA: DNA hybrid. Plus strand DNA synΛesis has been observed only after completion of Λe minus strand, and initiates at a unique site close to Λe 5' end of Λe minus strand. Complete elongation of Λe plus strand is not a requirement for coating and export of Λe nucleocapsid cores, Λus most extracellular virions contain incomplete plus strands and a large single- stranded gap in Λeir genomes. Because Λe hepatitis virus genome is autonomous and does not utilize a DNA-to-DNA paΛway for its replication, continuous intracellular replication of its genome is essential for Λe maintenance of Λe virus. The hepatitis B virus surface antigens (HBsAgs), which make up Λe viral envelope, are polypeptides encoded by Λe pre-Sl, pre-S2 and S genes of Λe virus. The major protein is Λe 226 amino acid S gene product derived from a 2.1 kb subgenomic message. As demonstrated by Λe following example, SEGS have been designed which target HBV nucleic acid, and inhibit replication, leading to decreased viral loads. B. Delivery of SEGS Molecules Two meΛods of delivery may be employed, (1) delivery of synΛetic SEGS molecules, or (2) delivery of a vector expressing SEGS molecules in a transient fashion. The meΛod of choice will be determined in preclinical studies, using standard meΛodology, and it is possible Λat Λey may be used in combination. Both of Λem can be efficiently delivered, for example, by using cationic liposome preparations. A variety of non-vector methods are available for delivering SEGS molecules to cells. For example, in general, the SEGS molecules, or DNA sequences encoding the SEGS molecules, can be incorporated within or on microparticles. As used herein, microparticles include liposomes, virosomes, microspheres and microcapsules formed of synthetic and/or natural polymers. MeΛods for making microcapsules and microspheres are known to Λose skilled in Λe art and include solvent evaporation, solvent casting, spray drying and solvent extension. Examples of useful polymers which can be incorporated into various microparticles include polysaccharides, poly anhydrides, polyorthoesters, polyhydroxides and proteins and peptides. Liposomes can be produced by standard meΛods such as Λose reported by Kim et al , Biochim. Biophys. Acta, 728:339-348 (1983); Liu et al , Biochim. Biophys. Acta, 1104:95-101 (1992); and Lee et al , Biochim. Biophys. Acta., 1103:185-197 (1992); Wang et al , Biochem., 28:9508-9514 (1989)). SEGS molecules or DNA encoding such molecules, can be encapsulated wiΛin liposomes when the molecules are present during Λe preparation of Λe microparticles. Briefly, Λe lipids of choice, dissolved in an organic solvent, are mixed and dried onto Λe bottom of a glass tube under vacuum. The lipid film is rehydrated using an aqueous buffered solution of Λe SEGS molecules, DNA encoding SEGS molecules to be encapsulated, and Λe resulting hydrated lipid vesicles or liposomes encapsulating Λe material can Λen be washed by centrifugation and can be filtered and stored at 4°C. This meΛod has been used to deliver nucleic acid molecules to Λe nucleus and cytoplasm of cells of Λe MOLT-3 leukemia cell line (Thierry and Dritschilo, Nucl. Acids Res. , 20:5691-5698 (1992)). Alternatively, SEGS molecules, or DNA encoding such molecules, can be incorporated within microparticles, or bound to Λe outside of Λe microparticles, eiΛer ionically or covalently. Cationic liposomes or microcapsules are microparticles that are particularly useful for delivering negatively charged compounds such as nucleic acid-based compounds, which can bind ionically to the positively charged outer surface of Λese liposomes. Various cationic liposomes have previously been shown to be very effective at delivering nucleic acids or nucleic acid-protein complexes to cells boΛ in vitro and in vivo, as reported by Feigner et al , Proc. Natl Acad. Sci. USA, 84:7413-7417 (1987); Feigner, Advanced Drug Delivery Reviews, 5:163-187 (1990); Clarenc et al , Anti-Cancer Drug Design, 8:81-94 (1993). Cationic liposomes or microcapsules can be prepared using mixtures including one or more lipids containing a cationic side group in a sufficient quantity such Λat Λe liposomes or microcapsules formed from Λe mixture possess a net positive charge which will ionically bind negatively charged compounds. Examples of positively charged lipids Λat may be used to produce cationic liposomes include Λe aminolipid dioleoyl phosphatidyl eΛanolamine (PE), which possesses a positively charged primary amino head group; phosphatidylcholine (PC), which possess positively charged head groups Λat are not primary amines; and N[l-(2,3-dioleyloxy)propyl]-N,N,N- trieΛylammonium ("DOTMA," see Feigner et al , Proc. Natl. Acad. Sci USA, 84:7413-7417 (1987); Feigner et al , Nature, 337:387-388 (1989); Feigner, Advanced Drug Delivery Reviews, 5:163-187 (1990)). A preferred form of microparticle for delivery of SEGS molecules are heme-bearing microparticles. In Λese microparticles, heme is intercalated into or covalently conjugated to Λe outer surface of Λe microparticles. Heme-bearing microparticles offer an advantage in Λat since Λey are preferentially bound and taken up by cells Λat express Λe heme receptor, such as hepatocytes, Λe amount of drug or oΛer compound required for an effective dose is significantly reduced. Such targeted delivery may also reduce systemic side effects that can arise from using relatively high drug concentrations in non-targeted delivery metaods. Preferred lipids for forming heme-bearing microparticles are l,2-dioleoyloxy-3-(trimethylammonium)propane (DOTAP) and dioleoyl phosphatidyl ethanolamine (DOPE). The production and use of heme-bearing microparticles are described in PCT application WO 95/27480 by Innovir. Nucleic acid can also be encapsulated by or coated on cationic liposomes which can be injected intravenously into a mammal. This system has been used to introduce DNA into Λe cells of multiple tissues of adult mice, including endoΛelium and bone marrow, where hematopoietic cells reside (see, for example, Zhu et al, Science, 261:209-211 (1993)). Liposomes containing eiΛer SEGS molecules or DNA encoding these molecules, can be administered systemically, for example, by intravenous or intraperitoneal administration, in an amount effective for delivery of Λe anti- hepatitis SEGS molecules to targeted cells. OΛer possible routes include trans-dermal or oral, when used in conjunction wiΛ appropriate microparticles. Generally, Λe total amount of Λe liposome-associated nucleic acid administered to an individual will be less than Λe amount of Λe unassociated nucleic acid Λat must be administered for Λe same desired or intended effect. AnoΛer useful delivery system is a complex of Λe SEGS wiΛ a cationic porphyrin, which protects as well as targets Λe SEGS to hepatocytes following injection. The system is extremely simple, since Λe two principle components are a porphyrin having a net overall positive charge, and Λe SEGS to be delivered, which has a net overall negative charge. The porphyrin binds Λe SEGS to be delivered and selectively targets Λe compound to cells preferentially binding Λe porphyrin. Compositions including various polymers such as Λe polylactic acid and polyglycolic acid copolymers, polyeΛylene, and polyorthoesters and Λe anti-hepatitis SEGS molecules, or DNA encoding such molecules, can be delivered locally to Λe appropriate cells by using a caΛeter or syringe. OΛer means of delivering such compositions locally to cells include using infusion pumps (for example, from Alza Corporation, Palo Alto, California) or incorporating Λe compositions into polymeric implants (see, for example, Johnson and Lloyd-Jones, eds. , Drug Delivery Systems (Chichester, England: Ellis Horwood Ltd., 1987), which can effect a sustained release of the therapeutic anti-hepatitis SEGS compositions to Λe immediate area of Λe implant. SEGS can also be applied topically, for example for Λe treatment of psoriasis or opΛalmic disorders, in a suitable topical carrier such as an ointment, salve, buffered saline solution, or other pharmaceutically acceptable topical or ophthalmic carrier. The following examples are presented for illustrative purposes and additional guidance. EXAMPLES Example 1: Oligonucleotide Synthesis, Plasmids and Transcription Reactions for Construction and Analysis of SEGS Molecules. Oligonucleotides: Oligoribonucleotides (RNA) were prepared according to the method of Ogilvie et al , Proc. Natl. Acad. Sci. U.S.A., 85:5764-5768 (1988), employing 5'-dimethoxytrityl-2'-meΛylsilyl- ribonucleoside 3'-CE-phosphoramidites (Biosearch, MA, or ChemGenes Corp. , MA). 2'-O-meΛyl oligoribonucleotides (2'-O-meΛyl RNA) were synΛesized using RNA synΛesis protocols of, and amidites were purchased from, eiΛer Biosearch or Glen Research. SynΛeses were performed on a Millipore 8909 Experdite DNA/RNA synΛesizer. Controlled pore glass (CPG) were used as Λe solid support matrix. The coupling time was about 13 minutes. For Λe synΛeses of analogues containing phosphoroΛioate linkages, oxidation was replaced by sulfurization which was carried out using Beaucage reagent for 10 to 15 minutes. The average coupling yield, as assayed by trityl measurement, was 96 to 98%. Cleavage from the support, base and phosphate deprotection, and removal of Λe 2'-O-TBDMS group were performed as described by Scaringe et al , Nucleic Acids Research, 18:5433-5441 (1990). The crude oligonucleotides in TBAF solution were desalted on a Sephadex G-25 column prior to standard electrophoretic purification using 15-20% poly aery lamide/7 M urea gels. Product bands were visualized by UV- shadowing, cut out, and eluted from Λe gel matrix. The eluted oligomers were finally desalted on a C lg Sep-Pak cartridge and quantified by OD 260 measurement. Homogeneity of the purified analogues was checked by 5 '-end labeling or analytical HPLC. They can be further characterized by base composition analysis, as described by Seela and Kaiser, Nucleic Acids Res., 15:3113-3129 (1987), and Λe content of Λioate linkages quantitated by 31 P- NMR. Terminal modifications of Λe 3 '-end were made by starting Λe synΛesis from a modified CPG support containing an amino group. RNAse P Cleavage Assays: Cleavage reactions were carried out generally according to Λe procedure described by Yuan et al , Proc. Natl. Acad. Sci, USA, 89:8006-8010, (1992). Briefly, short substrate reactions were made up to a total volume of 31 μ in 50 mM Tris-HCl pH 7.4, 10 mM MgCl 2 , 25 mM KC1, 0.1 mM EDTA, wiΛ an SEGS concentration of 200- 400 nM, and a target molecule concentration of 50 nM or less. The reactions were incubated at 37 °C for 1 hour. After incubation, Λe reaction solution was mixed wiΛ loading buffer (98% formamide, 10 mM EDTA, 0.025% bromophenol blue). The cleaved substrate was separated from Λe uncleaved by electrophoresis on a 15% acrylamide gel containing 7 M urea. The bands were quantified on a Molecular Dynamics Phosphor imager. The bands corresponding to Λe RNA substrate and Λe resulting two cleavage products were counted from Λe dried gel using a Betascope gel analyzer (Betagen). RNAse P was purified by DEAE Sepharose chromatography and glycerol density gradient centrifugation essentially as described by Bartkiewicz et al, Genes Dev. 3:488-499 (1989). To test cleavage with a longer target RNA molecules generated by transcription, different reaction conditions were used. Reactions in a total volume of 10 μl contained 40 mM Tris-HCl (pH 7.4), 10 mM MgCl 2 , 1 mM spermidine 10 mM dithioΛreitol, 0.05 μg/μl nuclease-free bovine serum albumin, 0.01% (v/v) Triton-XlOO, 0.8 Units/μl RNASIN, 0.2 mM ATP, 0.2 mM GTP, 0.2 mM UTP, 0.2 mM CTP, 0.1 μCi/μl [α 32 P] CTP, 2 mM m 7 G(5')pppG, 0.06 μg/μl yeast RNA, 25 mM KC1, 3 Units T7 RNA polymerase, 250 nM SEGS, 1 μl of human RNAse P and 3 ng/μl linearized plasmid. Reactions were initiated by Λe addition of linearized plasmid and incubated for 30 minutes at 37°C. Reactions were terminated by Λe addition of 10 μl of 80% formamide, 10 mM EDTA, 0.1 % bromphenol blue. After heating for 2 minutes at 90 °C, samples were electrophoresed for 2 hours at 48 watts on a 5% denaturing polyacrylamide gel. After vacuum drying for 1 hour at 60°C, the gel was analyzed by phosphoimaging. The percentage of RNA substrate remaining in eiΛer assay was plotted as function of Λe SEGS concentration and Λe catalytic efficiency expressed as K ^ (where k^ is Λe rate constant of cleavage and K m is Λe Michaelis constant), the second order rate constant for Λe reaction of free SEGS and substrate. Following Λe meΛods of Heidenreich and Eckstein (J. Biol Chem. , 267:1904-1909 (1992), Λe efficiency of Λe cleavage reaction, ^/K m ), was determined using Λe formula -In F/t=(k cat /K tn )[C] where F is Λe fraction of RNA substrate left, t is Λe reaction time, and [C] is the SEGS concentration. Fetal Calf Serum Stability Assay: The nuclease resistance of modified SEGS molecules can be tested in a Fetal Calf Serum (FCS) Assay. It was reported by Shaw et al , Nucleic Acids Res. 19:747-750 (1991), Λat 10% FCS, when heated inactivated, mimics raΛer closely Λe human serum. The assay conditions are very similar to Λat previously described by Hoke et al , Nucleic Acids Res. 19:5743-5748 (1991) . Briefly, an SEGS analog to be tested is 5 '-end labeled wiΛ T4 polynucleotide kinase and [7- 35 S] ATP (Λis procedure can generate radiolabeled oligonucleotides which are resistant against dephosphorylation). The labeled SEGS is then purified by phenol/chloroform extraction, followed by a Sephadex G-25 spin-column filtration. The purified SEGS is mixed wiΛ cold SEGS and 10% heat- mactivated fetal calf serum (FCS) so Λat Λe final concentration of SEGS is about 5 μM. SEGS analogues are treated over a period of 24 hours. Aliquots are wiΛdrawn from Λe reaction mixture at different time points, mixed wiΛ 2X loading dye, heat inactivated at 90 °C for 3 min, Λen stored at -20°C. The results are analyzed on 12% polyacrylamide/7 M urea gels. Example 2: Activity of SEGS molecules in promoting RNAse P cleavage SEGS Constructs Modeled on tRNA: The activities of SEGS and model target RNA molecules having various sequences and structures modeled on tRNA sequences were tested. Activities were measured in terms of Λe percent of substrate cleaved in one hour, as described in Example 1. A comparison was made between a SEGS wiΛ T loop sequences appended onto Λe T recognition arm (SEGS 3; SEQ ID NO. 1; see Figure 2) and a SEGS wiΛout any appended sequence (SEGS 7; nucleotides 4-15 of SEQ ID NO. 1; see Figure 5). This was done, in part, to test wheΛer Λe T loop sequences oΛer Λan Λe UNR motif affect promotion of RNAse P-mediated cleavage in a SEGS. The SEGS molecules used are shown in Figure 5. The 15 nucleotide SEGS has appended T loop sequence and Λe 12 nucleotide SEGS does not. The activities of Λese two SEGS in promoting cleavage of a model substrate (T 10, also shown in Figures 2 and 5) are listed in rows one and two in Table 1. It is clear that Λe appended nucleotides have no significant effect on cleavage activity. The first column in Table 1 shows Λe sequence of Λe turn region and, in Λe case of these examples, a short tail sequence made up of five or six adenine nucleotides. This is indicated by (A) for those targets having six adenine nucleotides and (A)* for Λose targets having five adenine nucleotides. Table 1. Cleavage Activity of Different Turn Region Sequences Turn Region Sequence % Cleavage SEGS + Target Comments U U C G (A) 96 EGS 7 + T 10 12 nt SEGS U U C G (A) 91 EGS 3 + T 10 15 nt SEGS U U C A (A)* 96 EGS 3 + T 11 15 nt SEGS U C C G (A) 12 EGS 3 + T 12 15 nt SEGS U C G A (A)* 55 EGS 3 + T 13 15 nt SEGS U U U G (A) 19 EGS 3 + T 14 15 nt SEGS C U C G (A) 51 EGS 3 + T 15 15 nt SEGS U U C G (A) 45 EGS 6 + T 16 G-C pair adjacent to cleavage site changed to C-G pair C U G A (A) 26 EGS 7 + T 24 12 nt SEGS G A A A (A) 0 EGS 7 + T 25 12 nt SEGS G A G A (A) 2 EGS 7 + T 26 12 nt SEGS G U G A (A) 21 EGS 7 + T 27 12 nt SEGS U A C G (A) 16 EGS 7 + T 28 12 nt SEGS A U C A (A) 34 EGS 7 + T 29 12 nt SEGS A U C G (A) 25 EGS 7 + T 30 12 nt SEGS A U C U (A) 0 EGS 7 + T 31 12 nt SEGS U U C G (A) 49 EGS 7m +T 10 all 2'0-meΛyl U U C A (A)* 60 EGS 7m + T 11 all 2'0 meΛyl Effect of Sequence in the Turn Region and at the Cleavage Site on SEGS Activity: Various model target RNA molecules were designed differing only in Λe sequence of Λe turn region. The substrates have Λe same nucleotide sequence as target RNA T 10 (SEQ ID NO. 2) except for Λe turn region (nucleotides 33-36 of SEQ ID NO:2). The sequence in Λe turn region for each substrate is listed in Table 1. Activity was assayed using EGS 3 (SEQ ID NO. 1) or EGS 7 (nucleotides 4 to 15 of SEQ ID NO:l). The assays were performed as described above wiΛ 50 nM target RNA, 400 nM SEGS, and 3 μl RNAse P. The activity of these SEGS are shown in rows 2-7 and 9-18 in Table 1. Nearly all of Λe variants are actively cleaved to a significant extent. In Λese examples, particular sequences are less favorable Λan oΛers, such as GAAA and AUCU. These results confirm Λat SEGS can be designed for target sequences having a wide range of sequences 3' of Λe second target region. The nucleotide at Λe 3' end of Λe A recognition arm (which is involved in Λe base pair adjacent to the cleavage site) of SEGS EGS 3 was changed from a cytidine nucleotide to a guanine nucleotide. The target RNA sequence was correspondingly changed. The activity of Λe resulting SEGS (EGS 6) is shown in row eight of Table 1. This activity (45 % cleavage), while lower Λan Λe SEGS with a cytidine nucleotide (row two in Table 1), is still significant. This indicates that while a cytidine nucleotide at the 3' end of Λe A recognition arm is preferable, it is not required. While Λe variant turn region and 3' end sequences affected Λe activity of Λe SEGS, all had measurable and useful activity. Effect of Chemical Modifications on SEGS Activity: 2' 0-meΛyl- oligoribonucleotides have several favorable features as a logical choice to modify. The synΛesis of Λese analogues is very similar to Λat of Λe DNA synΛesis. They have a much better binding affinity to RNA target Λan DNA analogues and Λe resulting duplexes have a structure between Λat of a RNA-RNA duplex (A-form) and DNA-DNA duplex (B-form). In addition, Λey prove to be fairly resistant to degradation by eiΛer RNA- or DNA- specific nucleases. 2'-0-meΛyl-oligoribonucleotide SEGS were made modeled on EGS 7 (nucleotide 4-15 of SEQ ID NO. 1). The activities of Λis chemically modified SEGS wiΛ two substrates are shown in rows 19 and 20 in Table 1. These activities, while lower than activities obtained wiΛ unmodified SEGS (compare wiΛ rows one and three in Table 1), are still significant. This indicates Λat a SEGS can have all of its nucleotides chemically modified and still retain significant activity. Effect of Length of Recognition Arms and Bulge Region on SEGS Activity: To gauge Λe effects of the lengΛ of the recognition arms and Λe bulge region, various SEGS and model target RNAs were constructed having different combinations of lengΛs for Λese regions. The substrates were modeled after target RNA T 10. The SEGS molecules were modeled after EGS 7. The assays were performed as described above wiΛ 33 nM target RNA, 333 nM SEGS, and 3 μl RNAse P. The lengΛ combinations tested, and Λe activity observed, are shown in Table 2. The starting lengΛs to which changes were made were a 7 base pair A stem, a 5 base pair T stem, and a 9 nucleotide bulge region. This combination has a high activity (see row one in Table 2). Table 2. Cleavage Activity of Different Constructs Base Pairs Base Pairs Nucleotides % in A Stem in T Stem in Bulge Cleavage Construct 7 5 9 92 T 10 + EGS 7 8 5 9 91 T 10 + EGS 9 9 5 9 36 T 10 + EGS 10 10 5 9 10 T 10 + EGS 11 7 6 9 93 T 17 + EGS 8 7 7 9 10 T 18 + EGS 5 8 6 9 23 T 17 + EGS 12 7 5 7 95 T 19 + EGS 7 7 5 11 92 T 20 + EGS 7 7 5 13 95 T 21 + EGS 7 7 5 15 92 T 22 + EGS 7 The first group of rows in Table 2 (rows one to four) show results wiΛ A stem lengΛs of 7, 8, 9, and 10 base pairs. All are active, alΛough Λe SEGS wiΛ 10 nucleotides in Λe A recognition arm is less active. This indicates that an A recognition arm of 7, 8, or 9 nucleotides is preferable. The second group of rows in Table 2 (rows five to seven) show results wiΛ T stem lengΛs of 6 and 7 base pairs. Row seven combines an 8 base pair A stem wiΛ a 6 base pair T stem. All are active, alΛough Λe SEGS wiΛ 7 nucleotides in Λe T recognition arm is less active. This indicates that an T recognition arm of 5 or 6 nucleotides is preferable. The Λird group of rows in Table 2 (rows eight to eleven) show results wiΛ bulge region lengΛs of from 7 to 15 nucleotides. All of these constructs are highly active. This indicates that Λe lengΛ of Λe bulge region is not a significant determinant of SEGS activity. Overall, Λese results indicate that an A recognition arm of 7 nucleotides and a T recognition arm of 5 nucleotides are most preferred. While Λese changes affect Λe activity of Λe SEGS, most changes had little effect and all of Λe SEGS had measurable and useful activity. Comparison of SEGS Activity and Activity of RNAse P substrates: The cleavage activities of minimal RNAse P substrates forming structures similar to SEGS/target RNA complexes were compared to Λe activity of SEGS molecules. RNAse P substrates are single nucleotide molecules containing boΛ Λe RNAse P cleavage site and a guide sequence. Unlike SEGS/target RNA complexes, RNAse P substrate have an intact T loop. Figures 12 and 13 show a minimal RNAse P substrate and a SEGS/target RNA complex, respectively. BoΛ are modeled on Λe sequence of tRNA Tyr . In RNAse P activity assays as described in Example 1, Λe RNAse P substrate was 99% cleaved in one hour and Λe SEGS promoted cleavage of 95% of Λe target RNA. RNAse P substrates and SEGS/target RNA pairs were also modeled after HBV sequences. Figures 3 and 6 show examples of such a SEGS/target RNA pair and an RNAse P substrate, respectively. In RNAse P activity assays as described in Example 1, Λe RNAse P substrate was 80% cleaved in one hour and Λe SEGS promoted cleavage of 65% of Λe target RNA. These results show Λat SEGS/target RNA complexes retain a significant fraction of the activity present in RNAse P substrates containing a T loop, even in Λe case of SEGS modeled after arbitrary sequences. Example 3: Construction and Activity of SEGS Molecules Promoting RNAse P Cleavage of HBsAg RNA SEGS molecules were designed to promote cleavage by RNAse P in RNA encoding HBsAg. In Λe presence of target, the SEGS molecules formed a structure similar to Λe A stem and T stem of tRNA which elicited cleavage by RNAse P. SEGS Constructs Targeted to HBsAg: SEGS sequences HBV B (SEQ ID NO. 6), HBV C (SEQ ID NO. 8), HBV FI (SEQ ID NO. 10), HBV H (SEQ ID NO. 12), and HBV HI (SEQ ID NO. 14) were designed to target regions of RNA encoding hepatitis B surface antigen (HBsAg). The regions were chosen as described earlier by identifying Λe location of UNR motifs in HBsAg-encoding RNA. As shown in Figure 7, Λe sequence of one of the recognition arms (Λe A recognition arm; nucleotides 6-13 of SEQ ID NO. 6) of SEGS HBV B is complementary to eight nucleotides in Λe sequence encoding HBsAg (nucleotides 13-20 of SEQ ID No. 7; nucleotides 387-394 of Λe 2.1 kb HBV transcript). The sequence of the oΛer recognition arm (Λe T recognition arm; nucleotides 1-5 of SEQ ID NO. 6) of SEGS HBV B is complementary to five nucleotides in Λe sequence encoding HBsAg (nucleotides 30-34 of SEQ ID No. 7; nucleotides 404-408 of Λe 2.1 kb HBV transcript). Thus, Λe target sequence contains two regions (Λe first and second target regions) complementary to Λe two recognition arms of Λe SEGS which are separated by 9 unpaired nucleotides (Λe bulge region). 2'-O-methyl-containing SEGS molecules: The SEGS molecules targeting HBV were prepared containing 2'-O-meΛyl nucleotides. These oligonucleotides were prepared in an automated oligonucleotide synΛesizer as described earlier except Λat Λe nucleotide reagents contained a 2'-O-meΛyl group. The average coupling yield, as assayed by trityl measurements, was in Λe range of 96 to 98%. Upon completion of deprotection, fully deprotected oligonucleotides were purified by denaturing gel electrophoresis and Λeir purity assessed by 5 '-end labeling, analytical HPLC, base composition analysis and 31 P-NMR. Cleavage of Large Target RNA Promoted by SEGS: The SEGS specific for HBV RNA sequences were assayed using Λe RNAse P cleavage assays described in Example 1 to determine Λe efficiency of Λe cleavage reaction. For Λis, plasmid pAYW2.1, containing Λe sequence Λat encodes Λe 2.1 kb RNA of Λe AYW strain of HBV, was linearized by digestion wiΛ Not I, and Λen transcribed by T7 RNA polymerase in the presence of [α 32 P]CTP. Labeled transcripts were incubated for 30 minutes at 37 °C wiΛ RNAse P in Λe presence of various SEGS molecules. Reaction products were subjected to denaturing polyacrylamide gel electrophoresis, and analyzed by phosphoimaging. Each of Λe SEGS specific for HBV RNA described above produced a visible cleavage band on Λe gel image. This indicates Λat SEGS designed for arbitrary target sequences in large, natural target RNA molecules are functional. Example 4: In vivo Efficacy of Short External Guide Sequences This example demonstrates Λat, when administered in vivo, a short external guide sequence is functional and has significant measurable effects on markers of a target RNA. SEGS HBV B was used in this study. This SEGS induced cleavage of HBV HBsAg mRNA in presence of purified RNase P (see Example 3). For in vivo administration, SEGS HBV B was used alone (free) or complexed ionically to a porphyrin. Specifically, Λe SEGS was complexed with either tetra meso (n-meΛyl 4-pyridyl) porphine (TMP) or meso terra (trimethyl anilinium) porphine (TMA or anilinium). The complexed or free EGS was injected into transgenic mice expressing fully assembled HBV viral particles (Guidotti et al J. Virol 69:6158-6169 (1995)). These mice support replication of HBV in Λe liver and produce all markers of viral replication. Five mg/Kg body weight of SEGS HBV B was injected via Λe tail vein of Λe mouse every day for five days. The animals were sacrificed on Λe sixΛ day and Λe following markers of viral replication were analyzed. A. The level of DNA in HBV virions present in Λe blood of Λe animal was determined by a standard dot-blot assay (Guidotti et al). The level of viral DNA in Λe blood is a direct index of Λe viral titer. B. Viral DNA in Λe liver was determined by a standard SouΛern blot analysis. This is a direct index of the replication of Λe virus in Λe liver. C. The level of viral core particles in liver tissue sections was determined by immunocytochemistry. Reverse transcription of HBV RNA, which is an integral part of the replication process of the virus, takes place in Λe core particles. Hence a reduction in core particles is anoΛer index of increase in replication of Λe virus. D. Serum alanine aminotransferase (ALT) was measured to rule out any possibility of toxicity due to Λe administration of the drug. Liver damage causes an elevation in Λe levels of serum ALT. The results of these measurements (Table 3) demonstrate Λat SEGS molecules do have an effect in reducing HBV replication in vivo as seen by Λe reduction in viral DNA in blood, viral DNA replicative intermediates and core particles in Λe liver. Note especially Λat Λe HBV markers were reduced wheΛer or not Λe SEGS was complexed wiΛ a porphyrin carrier. This indicates that Λe in vivo activity of a SEGS does not require any particular or specialized mode of delivery. Note also Λat Λe serum ALT remains stable wiΛ all of Λe treatments indicating that no significant liver damage is caused by administration of the SEGS. It was previously shown that administration of TMP alone for 10 days at 5 mg/Kg body weight into similar mice via tae tail vein had no effect on HBV replication thereby confirming that Λe observed antiviral effect is not due to TMP. Table 3 Groups Viral DNA DNA Replication Core Particles Serum ALT (4 mice/group) (Blood) Intermediates (Liver) (Liver) % of control % of control Relative score Saline control 100 100 + + + + + Normal SEGS alone 17 52 + + Normal SEGS + TMP 32 59 + + Normal SEGS + anilinium Not 30 + Normal detectable SEQUENCE LISTING (1) GENERAL INFORMATION: (i) APPLICANTS: Innovir Laboratories, Inc. (ii) TITLE OF INVENTION: ' Short External Guide Sequences (iii) NUMBER OF SEQUENCES: 15 (iv) CORRESPONDENCE ADDRESS: (A) ADDRESSEE: Patrea L. Pabst (B) STREET: 2800 One Atlantic Center 1201 West Peachtree Street (C) CITY: Atlanta (D) STATE: Georgia (E) COUNTRY: USA (F) ZIP: 30309-3450 (v) COMPUTER READABLE FORM: (A) MEDIUM TYPE: Floppy disk (B) COMPUTER: IBM PC compatible (C) OPERATING SYSTEM: PC-DOS/MS-DOS (D) SOFTWARE: Patentin Release #1.0, Version #1.25 (vi) CURRENT APPLICATION DATA: (A) APPLICATION NUMBER: (B) FILING DATE: (C) CLASSIFICATION: (vii) PRIOR APPLICATION DATA: (A) APPLICATION NUMBER: 08/615,961 (B) FILING DATE: March 14, 1996 (C) CLASSIFICATION: (viii) ATTORNEY/AGENT INFORMATION: (A) NAME: Pabst, Patrea L. (B) REGISTRATION NUMBER: 31,284 (C) REFERENCE/DOCKET NUMBER: ILI115 (ix) TELECOMMUNICATION INFORMATION: (A) TELEPHONE: (404) 873-8794 (B) TELEFAX: (404) 873-8795 (2) INFORMATION FOR SEQ ID NO:l: (i) SEQUENCE CHARACTERISTICS: (A) LENGTH: 15 base pairs (B) TYPE: nucleic acid (C) STRANDEDNESS: single (D) TOPOLOGY: linear (ii) MOLECULE TYPE: RNA (iii) HYPOTHETICAL: NO (iv) ANTI-SENSE: NO (xi) SEQUENCE DESCRIPTION: SEQ ID NO:l: AAUCCUUCCC CCACC 15 (2) INFORMATION FOR SEQ ID NO:2: (i) SEQUENCE CHARACTERISTICS: (A) LENGTH: 43 base pairs (B) TYPE: nucleic acid (C) STRANDEDNESS: single (D) TOPOLOGY: linear (ii) MOLECULE TYPE: RNA (iii) HYPOTHETICAL: NO (iv) ANTI-SENSE: NO (xi) SEQUENCE DESCRIPTION: SEQ ID NO:2 : GCACGGAAUU CGGUGGGGCC AGCUCCUGAA GGUUCGAAAA AAA 43 (2) INFORMATION FOR SEQ ID NO:3 : (i) SEQUENCE CHARACTERISTICS: (A) LENGTH: 15 base pairs (B) TYPE: nucleic acid (C) STRANDEDNESS: single (D) TOPOLOGY: linear (ii) MOLECULE TYPE: RNA (iii) HYPOTHETICAL: NO (iv) ANTI-SENSE: NO (xi) SEQUENCE DESCRIPTION: SEQ ID NO:3: AAUCCACUGC ACUAG 15 (2) INFORMATION FOR SEQ ID NO:4: (i) SEQUENCE CHARACTERISTICS: (A) LENGTH: 43 base pairs (B) TYPE: nucleic acid (C) STRANDEDNESS: single (D) TOPOLOGY: linear (ii) MOLECULE TYPE: RNA (iii) HYPOTHETICAL: NO (iv) ANTI-SENSE: NO (xi) SEQUENCE DESCRIPTION: SEQ ID NO:4: GGCUCAGUUU ACUAGUGCCA UUUGUUCAGU GGUUCGAAAA AAA 43 (2) INFORMATION FOR SEQ ID NO:5: (i) SEQUENCE CHARACTERISTICS: (A) LENGTH: 51 base pairs (B) TYPE: nucleic acid (C) STRANDEDNESS: single (D) TOPOLOGY: linear (ii) MOLECULE TYPE: RNA (iii) HYPOTHETICAL: NO (iv) ANTI-SENSE: NO (xi) SEQUENCE DESCRIPTION: SEQ ID NO:5: GGCUCAGUUU ACUAGUGCCA UUUGUUCAGU GGUUCGAAUC CACUGCACUA G 51 (2) INFORMATION FOR SEQ ID NO:6: (i) SEQUENCE CHARACTERISTICS: (A) LENGTH: 13 base pairs (B) TYPE: nucleic acid (C) STRANDEDNESS: single (D) TOPOLOGY: linear (ii) MOLECULE TYPE: RNA (iii) HYPOTHETICAL: NO (iv) ANTI-SENSE: NO (xi) SEQUENCE DESCRIPTION: SEQ ID NO:6 : GAGGAAACGC CGC 13 (2) INFORMATION FOR SEQ ID NO:7 : (i) SEQUENCE CHARACTERISTICS: (A) LENGTH: 50 base pairs (B) TYPE: nucleic acid (C) STRANDEDNESS: single (D) TOPOLOGY: linear (ii) MOLECULE TYPE: RNA (iii) HYPOTHETICAL: NO (iv) ANTI-SENSE: NO (xi) SEQUENCE DESCRIPTION: SEQ ID NO:7 : CUGGAUGUGU CUGCGGCGUU UUAUCAUCUU CCUCUUCAUC CUGCUGCUAU 50 (2) INFORMATION FOR SEQ ID NO:8: (i) SEQUENCE CHARACTERISTICS: (A) LENGTH: 13 base pairs (B) TYPE: nucleic acid (C) STRANDEDNESS: single (D) TOPOLOGY: linear (ii) MOLECULE TYPE: RNA (iii) HYPOTHETICAL: NO (iv) ANTI-SENSE: NO (xi) SEQUENCE DESCRIPTION: SEQ ID NO:8: GGUUUGGGGA UAC 13 (2) INFORMATION FOR SEQ ID NO:9: (i) SEQUENCE CHARACTERISTICS: (A) LENGTH: 56 base pairs (B) TYPE: nucleic acid (C) STRANDEDNESS: single (D) TOPOLOGY: linear (ii) MOLECULE TYPE: RNA (iii) HYPOTHETICAL: NO (iv) ANTI-SENSE: NO (xi) SEQUENCE DESCRIPTION: SEQ ID NO:9: AGGAACCUCU AUGUAUCCCU CCUGUUGCUG UACCAAACCU UCGGACGGAA AUUGCA 56 (2) INFORMATION FOR SEQ ID NO:10: (i) SEQUENCE CHARACTERISTICS: (A) LENGTH: 13 base pairs (B) TYPE: nucleic acid (C) STRANDEDNESS: single (D) TOPOLOGY: linear (ii) MOLECULE TYPE: RNA (iii) HYPOTHETICAL: NO (iv) ANTI-SENSE: NO (xi) SEQUENCE DESCRIPTION: SEQ ID NO:10: CCACUGAUGG CAC 13 (2) INFORMATION FOR SEQ ID NO:11: (i) SEQUENCE CHARACTERISTICS: (A) LENGTH: 46 base pairs (B) TYPE: nucleic acid (C) STRANDEDNESS: single (D) TOPOLOGY: linear (ii) MOLECULE TYPE: RNA (iii) HYPOTHETICAL: NO (iv) ANTI-SENSE: NO (xi) SEQUENCE DESCRIPTION: SEQ ID NO:ll: CUCAGUUUAC UAGUGCCAUU UGUUCAGUGG UUCGUAGGGC UUUCCC 46 (2) INFORMATION FOR SEQ ID NO:12: (i) SEQUENCE CHARACTERISTICS: (A) LENGTH: 13 base pairs (B) TYPE: nucleic acid (C) STRANDEDNESS: single (D) TOPOLOGY: linear (ii) MOLECULE TYPE: RNA (iii) HYPOTHETICAL: NO (iv) ANTI-SENSE: NO (xi) SEQUENCE DESCRIPTION: SEQ ID NO:12: GCGAAGGUCC GGC 13 (2) INFORMATION FOR SEQ ID NO:13: (i) SEQUENCE CHARACTERISTICS: (A) LENGTH: 48 base pairs (B) TYPE: nucleic acid (C) STRANDEDNESS: single (D) TOPOLOGY: linear (ii) MOLECULE TYPE: RNA (iii) HYPOTHETICAL: NO (iv) ANTI-SENSE: NO (xi) SEQUENCE DESCRIPTION: SEQ ID NO:13: GCCUUCUCAU CUGCCGGACC GUGUGCACUU CGCUUCACCU CUGCACGU 48 (2) INFORMATION FOR SEQ ID NO:14: (i) SEQUENCE CHARACTERISTICS: (A) LENGTH: 13 base pairs (B) TYPE: nucleic acid (C) STRANDEDNESS: single (D) TOPOLOGY: linear (ii) MOLECULE TYPE: RNA (iii) HYPOTHETICAL: NO (iv) ANTI-SENSE: NO (xi) SEQUENCE DESCRIPTION: SEQ ID N0:14: GCGAAGACGG UCC 13 (2) INFORMATION FOR SEQ ID NO:15: (i) SEQUENCE CHARACTERISTICS: (A) LENGTH: 51 base pairs (B) TYPE: nucleic acid (C) STRANDEDNESS: single (D) TOPOLOGY: linear (ii) MOLECULE TYPE: RNA (iii) HYPOTHETICAL: NO (iv) ANTI-SENSE: NO (xi) SEQUENCE DESCRIPTION: SEQ ID NO:15: GCACGGAAUU CGGUGGGGCC AGCUCCUGAA GGUUCGAAUC CUUCCCCCAC C 51

Claims: We claim: 1. A Short External Guide Sequence comprising an oligonucleotide molecule comprising a recognition sequence complementary to regions of a targeted sequence in a target RNA molecule, wherein Λe recognition sequence comprises an A recognition arm and a T recognition arm, and Λe targeted sequence comprises, in order from 5' to 3', a first target region, a bulge region, and a second target region, wherein Λe A recognition arm is complementary to Λe first target region, Λe T recognition arm is complementary to Λe second target region, and Λe T recognition arm is located 5' of and adjacent to Λe A recognition arm in Λe Short External Guide Sequence, and wherein Λe Short External Guide Sequence promotes eukaryotic RNAse P-mediated cleavage of Λe target RNA molecule. 2. The Short External Guide Sequence of claim 1 wherein Λe A recognition arm is from 7 to 9 nucleotides long, Λe T recognition arm is from 5 to 7 nucleotides long, and Λe bulge region is from 1 to 30 nucleotides long. 3. The Short External Guide Sequence of claim 2 wherein Λe A recognition arm is 7 or 8 nucleotides long, Λe T recognition arm is 5 or 6 nucleotides long, and Λe bulge region is from 5 to 15 nucleotides long. 4. The Short External Guide Sequence of claim 1 wherein Λe targeted sequence further comprises a turn region wherein Λe turn region has a sequence of NUNR, where N is any nucleotide, R is any purine nucleotide, and U is a uridine nucleotide. 5. The Short External Guide Sequence of claim 1 wherein Λe turn region has a sequence of NUCR or UUNR. 6. The Short External Guide Sequence of claim 5 wherein Λe turn region has a sequence of UUCR. 7. The Short External Guide Sequence of claim 1 comprising a nucleotide base sequence selected from Λe group consisting of SEQ ID NO. 3, SEQ ID NO. 6, SEQ ID NO: 8, SEQ ID NO: 10, SEQ ID NO: 12, SEQ ID NO: 14. 8. The Short External Guide Sequence of claim 1 wherein Λe target RNA molecule is a hepatitis B RNA molecule. 9. A composition for promoting cleavage of a target RNA molecule wherein Λe composition comprises the Short External Guide Sequence of claim 1 in a pharmaceutically acceptable delivery system. 10. The composition of claim 9 wherein Λe pharmaceutically acceptable delivery system is selected from Λe group consisting of liposomes, virosomes, microspheres and microcapsules. 11. The Short External Guide Sequence of claim 1 wherein one or more of Λe 2' hydroxyl groups of ribonucleotides are replaced wiΛ a chemical group selected from Λe group consisting of hydrogen, an O-alkyl group, an O- allyl group, an amino group, and fluorine. 12. The Short External Guide Sequence of claim 1 wherein one or more of Λe phosphate linking groups are replaced wiΛ a linking group selected from Λe group consisting of meΛyl phosphonate and phosphorotaioate. 13. The Short External Guide Sequence of claim 1 wherein one or more of the 2' hydroxyl groups of ribonucleotides are replaced with a chemical group selected from Λe group consisting of hydrogen, an O-alkyl group, an O- allyl group, an amino group, and fluorine, and wherein one or more of Λe phosphate linking groups are replaced wiΛ a linking group selected from Λe group consisting of meΛyl phosphonate and phosphoroΛioate . 14. The Short External Guide Sequence of claim 13 wherein one or more of Λe 2' hydroxyl groups of Λe ribonucleotides are replaced wiΛ hydrogen or a meΛoxy group, and wherein one or more of Λe phosphate linking groups are replaced wiΛ phosphoroΛioate. 15. The Short External Guide Sequence of claim 1 wherein Λe 3' hydroxyl of Λe Short External Guide Sequence is replaced wiΛ a chemical group selected from Λe group consisting of -OPO(O)OCH 2 CH(OH)-CH 2 NH 2 , -OPO(S)OCH 2 CH(OH)CH 2 NH 2 , and -3'-thymine nucleotide. 16. The Short External Guide Sequence of claim 15 wherein Λe 3' hydroxyl of Λe Short External Guide Sequence is replaced with -3'-Λymine nucleotide. 17. A meΛod for cleaving a target RNA molecule comprising bringing into contact, under conditions Λat promote RNAse P-mediated cleavage, RNAse P, Λe target RNA molecule, and a Short External Guide Sequence which comprises an oligonucleotide molecule comprising a recognition sequence complementary to regions of a targeted sequence in a target RNA molecule, wherein Λe recognition sequence comprises an A recognition arm and a T recognition arm, and Λe targeted sequence comprises, in order from 5' to 3', a first target region, a bulge region, and a second target region, wherein Λe A recognition arm is complementary to Λe first target region, Λe T recognition arm is complementary to Λe second target region, and Λe T recognition arm is located 5' of and adjacent to Λe A recognition arm in Λe Short External Guide Sequence, and wherein Λe Short External Guide Sequence promotes eukaryotic RNAse P-mediated cleavage of Λe target RNA molecule. 18. The meΛod of claim 17 wherein Λe target RNA molecule is a viral RNA molecule, wherein Λe step of bringing into contact is accomplished by administering to a patient or cells from a patient Λe Short External Guide Sequence, and wherein Λe Short External Guide Sequence is in a pharmaceutically acceptable delivery system. 19. The meΛod of claim 18 wherein Λe pharmaceutically acceptable delivery system is selected from Λe group consisting of liposomes, virosomes, microspheres and microcapsules. 20. The meΛod of claim 18 wherein Λe viral RNA molecule is a hepatitis B RNA molecule. 21. A meΛod of inhibiting a virus comprising administering to a patient or cells from a patient an engineered expression vector encoding a Short External Guide Sequence, wherein Λe Short External Guide Sequence comprises an oligonucleotide molecule comprising a recognition sequence complementary to regions of a targeted sequence in a target RNA molecule, wherein Λe recognition sequence comprises an A recognition arm and a T recognition arm, and the targeted sequence comprises, in order from 5' to 3', a first target region, a bulge region, and a second target region, wherein the A recognition arm is complementary to Λe first target region, the T recognition arm is complementary to Λe second target region, and Λe T recognition arm is located 5' of and adjacent to Λe A recognition arm in Λe Short External Guide Sequence, and wherein Λe Short External Guide Sequence promotes eukaryotic RNAse P-mediated cleavage of Λe target RNA molecule. 22. The meΛod of claim 21 wherein Λe engineered expression vector is in a pharmaceutically acceptable delivery system. 23. The composition of claim 22 wherein Λe pharmaceutically acceptable delivery system is selected from Λe group consisting of liposomes, virosomes, microspheres and microcapsules. 24. The meΛod of claim 23 wherein the pharmaceutically acceptable delivery system is a liposome. 25. The meΛod of claim 21 wherein Λe vector is a viral vector selected from Λe group consisting of retroviral vectors, adeno-associated viral vectors and Epstein-Barr viral vectors. 26. An engineered expression vector encoding a Short External Guide Sequence comprising an oligonucleotide molecule comprising a recognition sequence complementary to regions of a targeted sequence in a target RNA molecule, wherein Λe recognition sequence comprises an A recognition arm and a T recognition arm, and Λe targeted sequence comprises, in order from 5' to 3', a first target region, a bulge region, and a second target region, wherein Λe A recognition arm is complementary to Λe first target region, Λe T recognition arm is complementary to Λe second target region, and the T recognition arm is located 5' of and adjacent to Λe A recognition arm in Λe Short External Guide Sequence, and wherein Λe Short External Guide Sequence promotes eukaryotic RNAse P-mediated cleavage of Λe target RNA molecule. 27. A composition for promoting cleavage of a hepatitis B RNA molecule wherein Λe composition comprises Λe engineered expression vector of claim 26 in a pharmaceutically acceptable delivery system. 28. The composition of claim 27 wherein Λe pharmaceutically acceptable delivery system is selected from Λe group consisting of liposomes, virosomes, microspheres and microcapsules. 29. The Short External Guide Sequence of claim 1 further comprising a RNA sequence binding to a ligand wherein Λe Short External Guide Sequence promotes cleavage of Λe target RNA molecule by RNAse P only when bound to Λe ligand. 30. The Short External Guide Sequence of claim 1 further comprising a RNA sequence binding to a ligand wherein Λe Short External Guide Sequence promotes cleavage of Λe target RNA molecule by RNAse P only when not bound to Λe ligand.

Inventors: GEORGE SHAJI T, MA MICHAEL, WERNER MARTINA, GEORGE, SHAJI, T., MA, MICHAEL, WERNER, MARTINA
Applicants: GEORGE SHAJI T, INNOVIR LAB INC, MA MICHAEL, WERNER MARTINA, GEORGE, SHAJI, T., INNOVIR LABORATORIES, INC., MA, MICHAEL, WERNER, MARTINA
Application year: 1997
Main classification: C12N15
IPC codes: A61K9, A61K31, A61K35, A61K38, A61K48, A61P31, C12N9, C12N15, C12Q1