SEQUENCING BY LIGATION OF ENCODED ADAPTORS

Abstract: The invention provides a method of nucleic acid sequence analysis based on the ligation of one or more sets of encoded adaptors to the terminus of a target polynucleotide. Encoded adaptors whose protruding strands form perfectly matched duplexes with the complementary protruding strands of the target polynucleotide are ligated, and the identity of the nucleotides in the protruding strands is determined by an oligonucleotide tag carried by the encoded adaptor. Such determination, or "decoding" is carried out by specifically hybridizing a labeled tag complement to its corresponding tag on the ligated adaptor.

Description: SEQUENCING BY LIGATION OF ENCODED ADAPTORS Field of the Invention The mvention relates generally to methods for determining the nucleotide sequence of a polynucleotide, and more particularly, to a method of identifying terminal nucleotides of a polynucleotide by specific hgation of encoded adaptors BACKGROUND The DNA sequencing methods of choice for nearly all scientific and commercial applications are based on the dideoxy chain termination approach pioneered by Sanger, e g Sanger et al, Proc Natl Acad Sci , 74 5463-5467 (1977) The method has been improved in several ways and, in a variety of forms, is used in all commercial DNA sequencing instruments, e g Hunkapiller et al, Science, 254 59-67 (1991) The chain termination method requires the generation of one or more sets of labeled DNA fragments, each having a common origin and each terminating with a known base The set or sets of fragments must then be separated by size to obtain sequence information The size separation is usually accomplished by high resolution gel electrophoresis. which must have the capacity of distinguishing very large fragments differing m size by no more than a single nucleotide Despite many significant improvements, such as separations with capillary arrays and the use of non-gel electrophoretic separation mediums, the technique does not readily lend itself to miniaturization or to massively parallel implementation As an alternative to the Sanger-based approaches to DNA sequencing, several so- called "basc-by-base" or "single base" sequencing approaches have been explored, e g Cheeseman, U S patent 5,302,509, Tsien et al, International application WO 91/06678, Rosenthal et al, International application WO 93/21340, Canard et al, Gene, 148 1-6 (1994), and Metzker et al, Nucleic Acids Research, 22 4259-4267 (1994) These approaches are characterized by the determination of a single nucleotide per cycle of chemical or biochemical operations and no requirement of a separation step Thus, if they could be implemented as conceived, "base-by-base" approaches promise the possibility of carrying out many thousands of sequencing reactions in parallel, for example, on target polynucleotides attached to microparticles or on solid phase arrays, e g International patent application PCT/US95/12678 (WO 96/12039) Unfortunateh . "base-by-base" sequencing schemes have not had widespread application because of numerous problems, such as inefficient chemistries which prevent determination of any more than a few nucleotides in a complete sequencing operation Moreover, in base-by-basc approaches that require enzymatic manipulations, further problems arise with instrumentation used for automated processing When a series of enzymatic steps are earned out in reaction chambers hav g high surface-to-volume ratios and narrow channel dimensions, enzymes may stick to surface components making washes and successive processmg steps very difficult The accumulation of protein also affects molecular reporter systems, particularly those employing fluorescent labels, and renders the interpretation of measurements based on such systems difficult and inconvenient These and similar difficulties have significantly slowed the application of "base-by-base" sequencmg schemes to parallel sequencmg efforts An important advance in base-by-base sequencing technology could be made, especially m automated systems, if an alternative approach was available for determining the terminal nucleotides of polynucleotides that minimized or eliminated repetitive processing cycles employing multiple enzymes Summary of the Invention Accordingly, an object of our invention is to provide a DNA sequencing scheme which does not suffer the drawbacks of current base-by-base approaches Another object of our invention is to provide a method of DNA sequencing which is amenable to parallel, or simultaneous, application to thousands of DNA fragments present m a common reaction vessel A further object of our invention is to provide a method of DNA sequencing which permits the identification of a terminal portion of a target polynucleotide with minimal enzymatic steps Yet another object of our invention is to provide a set of encoded adaptors for identifying the sequence of a plurality of terminal nucleotides of one or more target polynucleotides Our invention provides these and other objects by providing a method of nucleic acid sequence analysis based on the hgation of one or more sets of encoded adaptors to a terminus of a target polynucleotide (or to the termini of multiple target polynucleotides when used in a parallel sequencmg operation) Each encoded adaptor comprises a protruding strand and an oligonucleotide tag selected from a minimally cross-hybridizing set of oligonucleotides Encoded adaptors whose protruding strands form perfectly matched duplexes with the complementary protruding strands of the target polynucleotide are ligated After hgation, the identity and ordering of the nucleotides in the protruding strands are determined, or "decoded," by specifically hybridizing a labeled tag complement to its corresponding tag on the ligated adaptor For example, if an encoded adaptor with a protruding strand of four nucleotides, say 5'-AGGT, forms a perfectly matched duplex with the complementary protruding strand of a target polynucleotide and is ligated, the four complementary nucleotides, 3'-TCCA, on the polynucleotide may be identified by a umque oligonucleotide tag selected from a set of 256 such tags, one for every possible four nucleotide sequence of the protruding strands Tag complements are applied to the ligated adaptors under conditions which allow specific hybridization of only those tag complements that form perfectly matched duplexes (or tnplexes) with the oligonucleotide tags of the ligated adaptors The tag complements may be applied individually or as one or more mixtures to determine the identity of the oligonucleotide tags, and therefore, the sequences of the protruding strands As explained more fully below, the encoded adaptors may be used in sequence analysis either (l) to identify one or more nucleotides as a step of a process that involves repeated cycles of hgation, identification, and cleavage, as descπbed in Brenner U S patent 5,599,675 and PCT Publication No WO 95/27080, or (n) as a "stand alone" identification method, wherein sets of encoded adaptors are applied to target polynucleotides such that each set is capable of identifying the nucleotide sequence of a different portion of a target polynucleotide, that is, in the latter embodiment, sequence analysis is earned out with a s gle hgation for each set followed by identification An important feature of the encoded adaptors is the use of oligonucleotide tags that are members of a minimally cross-hybndizing set of oligonucleotides, e g as described in International patent applications PCT/US95/12791 (WO 96/12041) and PCT/US96/09513 (WO 96/41011) The sequences of oligonucleotides of such a set differ from the sequences of every other member of the same set by at least two nucleotides Thus, each member of such a set cannot form a duplex (or triplex) with the complement of anv other member with less than two mismatches Preferably, each member of a minimally cross-hybridizing set differs from every other member by as many nucleotides as possible consistent with the size of set required for a particular application For example, where longer oligonucleotide tags are used, such as 12- to 20-mers for delivering labels to encoded adaptors, then the difference between members of a minimally cross-hybridizing set is preferably significantly greater than two Preferably, each member of such a set differs from every other member by at least four nucleotides More preferably, each member of such a set differs from every other member by at least six nucleotides Complements of oligonucleotide tags of the invention are referred to herein as "tag complements " Oligonucleotide tags may be single stranded and be designed for specific hybridization to smgle stranded tag complements by duplex formation Oligonucleotide tags may also be double stranded and be designed for specific hybridization to single stranded tag complements by tnplex formation Preferably, the oligonucleotide tags of the encoded adaptors are double stranded and their tag complements are smgle stranded, such that specific hybridization of a tag with its complements occurs through the formation of a tnplex structure Preferably, the method of the invention comprises the following steps (a) ligating an encoded adaptor to an end of a polynucleotide, the adaptor having an oligonucleotide tag selected from a minimally cross-hybndizing set of oligonucleotides and a protruding strand complementary to a protrudmg strand of the polynucleotide, and (b) identifying one or more nucleotides in the protrudmg strand of the polynucleotide by specifically hybridizing a tag complement to the oligonucleotide tag of the encoded adaptor Bnef Descnption of the Drawings Figures 1A-1E diagrammatically illustrate the use of encoded adaptors to determine the terminal nucleotides sequences of a plurality of tagged polynucleotides Figure 2 illustrates the phenomena of self-hgation of identical polynucleotides that are anchored to a solid phase support Figure 3 A illustrates steps in a preferred method of the invention in which a double stranded adaptor havmg a blocked 3' carbon is ligated to a target polynucleotide Figure 3B illustrates the use of the preferred embodiment in a method of DNA sequencing by stepwise cycles of hgation and cleavage Figure 4 illustrates data from the determination of the terminal nucleotides of a test polynucleotide usmg the method of the present invention Figure 5 is a schematic representation of a flow chamber and detection apparatus for observing a planar array of microparticles loaded with cDNA molecules for sequencmg Definitions As used herein, the term "encoded adaptor" is used synonymously with the term "encoded probe" of pnonty document U S patent application Ser No 08/689,587 As used herein, the term "hgation" means the formation of a covalent bond between the ends of one or more (usually two) oligonucleotides The term usually refers to the formation of a phosphodiester bond resulting from the following reaction, which is usually catalyzed by a hgase ohgo 1 (5')-OP(0-)(=0)0 + HO-(3 , )ohgθ2-5' → ohgo 1 (5')-OP(0-)(=0)0-(3 , )olιgθ2-5' where o goi and o gθ2 are either two different oligonucleotides or different ends of the same oligonucleotide The term encompasses non-enzymatic formation of phosphodiester bonds, as well as the formation of non-phosphodiester covalent bonds between the ends of oligonucleotides, such as phosphorothioate bonds, disulfide bonds, and the like A hgation reaction is usually template dπven, in that the ends of o goj and ohgθ2 are brought into juxtaposition by specific hybndization to a template strand A special case of template-driven hgation is the hgation of two double stranded oligonucleotides havmg complementary protruding strands "Complement" or "tag complement" as used herein in reference to oligonucleotide tags refers to an oligonucleotide to which a oligonucleotide tag specifically hybridizes to form a perfectly matched duplex or tnplex In embodiments where specific hybridization results in a tnplex, the oligonucleotide tag may be selected to be either double stranded or smgle stranded Thus, where triplexes are formed, the term "complement" is meant to encompass either a double stranded complement of a smgle stranded oligonucleotide tag or a smgle stranded complement of a double stranded oligonucleotide tag The term "oligonucleotide" as used herem mcludes linear o gomers of natural or modified monomers or linkages, including deoxynbonucleosides, nbonucleosides, anomenc forms thereof, peptide nucleic acids (PNAs), and the like, capable of specifically binding to a target polynucleotide by way of a regular pattern of monomer-to-monomcr interactions, such as Watson-Cπck type of base pairing, base stacking, Hoogsteen or reverse Hoogsteen types of base pairing, or the like Usually monomers are linked by phosphodiester bonds or analogs thereof to form oligonucleotides ranging in size from a few monomeπc units, e g 3-4, to several tens of monomeric units, e g 40-60 Whenever an oligonucleotide is represented by a sequence of letters, such as "ATGCCTG," it will be understood that the nucleotides are m 5'— >3' order from left to right and that "A" denotes deoxyadenosme, "C" denotes deoxycytidine, "G" denotes deoxyguanosine, and "T" denotes thymidme, unless otherwise noted Usually oligonucleotides of the invention compnse the four natural nucleotides, however, they may also comprise non-natural nucleotide analogs It is clear to those skilled in the art when oligonucleotides having natural or non-natural nucleotides may be employed, e g where processing by enzymes is called for, usually oligonucleotides consistmg of natural nucleotides are required "Perfectly matched" in reference to a duplex means that the poly- or oligonucleotide strands making up the duplex form a double stranded structure with one other such that every nucleotide in each strand undergoes Watson-Crick basepairing with a nucleotide in the other strand The term also comprehends the pairmg of nucleoside analogs, such as deoxyinosine, nucleosides with 2-amιnopuπne bases, and the like, that may be employed In reference to a tnplex, the term means that the tnplex consists of a perfectly matched duplex and a third strand in which every nucleotide undergoes Hoogsteen or reverse Hoogsteen association with a basepair of the perfectly matched duplex Conversely, a "mismatch" in a duplex between a tag and an oligonucleotide means that a pair or triplet of nucleotides in the duplex or triplex fails to undergo Watson-Crick and/or Hoogsteen and/or reverse Hoogsteen bonding As used herem. "nucleoside" includes the natural nucleosides, including 2'-deoxy and 2'-hydroxyl forms, e g as descπbed in Kornberg and Baker, DNA Replication, 2nd Ed (Freeman, San Francisco, 1992) "Analogs" in reference to nucleosides mcludes synthetic nucleosides havmg modified base moieties and or modified sugar moieties, e g described by Scheit, Nucleotide Analogs (John Wiley, New York, 1980), Uhlman and Peyman, Chemical Reviews, 90 543-584 (1990), or the like, with the only proviso that they are capable of specific hybridization Such analogs include synthetic nucleosides designed to enhance binding properties, reduce complexity, mcrease specificity, and the like As used herem "sequence determination" or "determining a nucleotide sequence" in reference to polynucleotides mcludes determination of partial as well as full sequence information of the polynucleotide That is, the term mcludes sequence compansons, fingerpnnting, and like levels of information about a target polynucleotide, as well as the express identification and ordering of nucleosides, usually each nucleoside, m a target polynucleotide The term also mcludes the determination of the identification, ordering, and locations of one, two, or three of the four types of nucleotides within a target polynucleotide For example, m some embodiments sequence determination may be effected by identifying the ordering and locations of a single type of nucleotide, e g cytosmes, within the target polynucleotide "CATCGC " so that its sequence is represented as a binary code, e g " 100101 " for "C-(not C)-(not C)-C-(not C)-C " and the like As used herem, the term "complexity" in reference to a population of polynucleotides means the number of different species of molecule present in the population DETAILED DESCRIPTION OF THE INVENTION The invention involves the hgation of encoded adaptors specifically hybridized to the terminus or termini of one or more target polynucleotides Sequence information about the region where specific hybridization occurs is obtained by "decoding" the oligonucleotide tags of the encoded adaptors thus ligated In one aspect of the invention, multiple sets of encoded adaptors are ligated to a target polynucleotide at staggered cleavage points so that the encoded adaptors provide sequence information from each of a plurality of portions of the target polynucleotide Such portions may be disjoint, overlapping or contiguous, however, preferably, the portions are contiguous and together permit the identification of a sequence of nucleotides equal to the sum of the lengths of the individual portions In this aspect, there is only a smgle hgation of encoded adaptors followed by identification by "de-codmg" the tags of the ligated adaptors In another aspect of the invention, encoded adaptors are employed as an identification step in a process involving repeated cycles of hgation, identification, and cleavage, desenbed more fully below In the latter embodiment, the invention makes use of nucleases whose recognition sites are separate from their cleavage sites Preferably, such nucleases are type Ils restnction endonucleases The nucleases are used to generate protruding strands on target polynucleotides to which encoded adaptors are ligated The amount of sequence information obtained in a given embodiment of the mvention depends in part on how many such nucleases are employed and the length of the protruding strand produce upon cleavage An important aspect of the invention is the capability of sequencing many target polynucleotides in parallel In this aspect, the method of the invention comprises the following steps (a) attaching a first oligonucleotide tag from a repertoire of tags to each polynucleotide in a population of polynucleotides such that each first oligonucleotide tag from the repertoire is selected from a first minimally cross-hybndizing set, (b) sampling the population of polynucleotides such that substantially all different polynucleotides m the population have different first oligonucleotide tags attached, (c) gating one or more encoded adaptors to an end of each of the polynucleotides in the population, each encoded adaptor havmg a second oligonucleotide tag selected from a second minimally cross-hybndizmg set and a protrudmg strand complementary to a protruding strand of a polynucleotide of the population, (d) sorting the polynucleotides of the population by specifically hybndizmg the first oligonucleotide tags with their respective complements, the respective complements being attached as umform populations of substantially identical oligonucleotides in spatially discrete regions on the one or more solid phase supports, and (e) identifying one or more nucleotides m said protrudmg strands of the polynucleotides by specifically hybndizmg a tag complement to each second oligonucleotide tag of the one or more encoded adaptors In this embodiment, the one or more encoded adaptors may be ligated to an end of the polynucleotides either before or after the polynucleotides have been sorted onto solid phase supports by the first oligonucleotide tags In the preferred embodiment, encoded adaptors include a type Ils restriction endonuclease site which permits the encoded adaptors to be cleaved from the polynucleotides and the polynucleotides shortened after sequence identification In accordance with the preferred embodiment, the method further mcludes repeated cycles of hgation, identification, and cleavage, such that one or more nucleotides are identified in each cycle Preferably, from 2 to 6 nucleotides are identified and their ordering determined m each cycle Sequence Analysis without Cycles of Ligation and Cleavage Sequence analysis without cycles of hgation and cleavage in accordance with the mvention is illustrated by the embodiment of Figures 1A through IE In this embodiment, k target polynucleotides are prepared as described below, and also in Brenner, International patent applications PCT/US95/ 12791 (WO 96/12041) and PCT/US96/09513 (WO 96/41011) That is, a sample is taken from a population of polynucleotides conjugated with oligonucleotide tags designated by small "t's " These tags are sometimes referred to as oligonucleotide tags for sorting, or as "first" oligonucleotide tags The tag-polynuclcotide conjugates of the sample are amplified, e g by polymerase chain reaction (PCR) or by cloning, to give 1 through k populations of conjugates, indicated by (14)-(18) in Fig 1A Preferably, the ends of the conjugates opposite of the (small "t") tags are prepared for hgating one or more adaptors, each of which contains a recognition site for a nuclease whose cleavage site is separate from its recognition site In the illustrated embodiment, three such adaptors, referred to herein as "cleavage adaptors," are employed The number of such adaptors employed depends on several factors, mcludmg the amount of sequence information desired, the availability of type Ils nucleases with suitable reaches and cleavage characteristics, and the like Preferably, from one to three cleavage adaptors are used, and the adaptors are design to accommodate different type Ils nucleases capable of generating protrudmg strands of at least four-nucleotides after cleavage If the method of the mvention is be g applied to signature sequencing of a cDNA population, then prior to hgation of the cleavage adaptors, the tag-polynucleotide conjugates may be cleaved with a restriction endonuclease with a high frequency of recogmtion sites, such as Taq I, Alu I, HmPl I, Dpn II, Nla III, or the like For enzymes, such as Alu I, that leave blunt ends, a staggered end may be produced with T4 DNA polymerase, e g as described in Brenner, International patent application PCT/US95/ 12791 cited above, and Kuijper et al, Gene, 112 147-155 (1992) If the target polynucleotides are prepared by cleavage with Taq I, then the following ends are available for hgation cgannnn . . . -3 ' tnnnn . . . -5 ' Thus, an exemplary set of three cleavage adaptors may be constructed as follows ;i) NN ... NGAAGA cgannnnnnnnnnnnnnnnnnn ... -3 NN ... NCTTCTGCp tnnnnnnnnnnnnnnnnnnn ... -5 (2) NN ... NGCAGCA cgannnnnnnnnnnnnnnnnnn ... -3 NN ... NCGTCGTGCp tnnnnnnnnnnnnnnnnnnn ... -5 (3) NN ... NGGGA cgannnnnnnnnnnnnnnnnnn ... -3' NN ... NCCCTGCp tnnnnnnnnnnnnnnnnnnn ... -5 ' where cleavage adaptors (1), (2), and (3) are shown in capital letters with the respective recogmtion sites of nucleases Bbs I, Bbv I, and Bsm FI underlined and a 5' phosphate mdicated as "p " The double underlmed portions of the target polynucleotide indicate the positions of the protrudmg strands after hgation and cleavage In all cases, the target polynucleotide is left with a 5' protruding strand of four nucleotides Clearly, many different embodiments can be constructed usmg different numbers and kinds of nucleases As discussed in Brenner, U.S. patent 5,599,675 and WO 95/27080, preferably pnor to cleavage, internal Bbs I, Bbv I, and Bsm FI sites are blocked, e.g. by methylation, to prevent undesirable cleavages at internal sites of the target polynucleotide. Returning to the illustrated embodiment, cleavage adaptors A], A2, and A3 are ligated (20) m a concentration ratio of 1 : 1 : 1 to the k target polynucleotides to give the conjugates shown in Fig. IB, such that within each population of tag-polynucleotide conjugates there are approximately equal numbers of conjugates having A\, A2, and A3 attached. After hgation (20), the target polynucleotides are successively cleaved with each of the nucleases of the cleavage adaptors and ligated to a set of encoded adaptors. First, the target polynucleotides are cleaved (22) with the nuclease of cleavage adaptor A j after which a first set of encoded adaptors are ligated to the resulting protruding strands. The cleavage results in about a third of the target polynucleotides of each type, i.e. tj, t2, ... t j ., being available for ligation. Preferably, the encoded adaptors are applied as one or more mixtures of adaptors which taken together contain every possible sequence of a protruding strand. Reaction conditions are selected so that only encoded adaptors whose protruding strands form perfectly matched duplexes with those of the target polynucleotide arc ligated to form encoded conjugates (28), (30), and (32) (Fig. IC). The capital "T's" with subscripts indicate that unique oligonucleotide tags are carried by the encoded adaptors for labeling. The oligonucleotide tags carried by encoded adaptors are sometimes referred to tags for delivering labels to the encoded adaptors, or as "second" oligonucleotide tags. As decribed more fully below, single stranded oligonucleotide tags used for sorting preferably consist of only three of the four nucleotides, so that a T4 DNA polymerase "stripping" reaction, e.g. Kuijper et al (cited above), can be used to prepare target polynucleotides for loading onto solid phase supports. On the other hand, oligonucleotide tags employed for delivering labels may consist of all for nucleotides. As mentioned above, encoded adaptors comprise a protruding strand (24) and an oligonucleotide tag (26). Thus, if the "Aj" cleavage of the t] -polynucleotide conjugates results in the following ends: 5 ' - . . . nnnnnnnnn 3 ' - . . . nnnnnnnnnacct then oligonucleotide tag T24 could have the following structure (SEQ ID NO: 1): tggattctagagagagagagagagagag -3' aagatctctctctctctctctctc where the double stranded portion may be one of a set of 48 (=12 nucleotide positions x 4 kinds of nucleotide) double stranded 20-mer oligonucleotide tags that forms a perfectly matched tnplex with a unique tag complement and forms a triplex with at least 6 mismatches with all other tag complements The encoded adaptors in this example may be ligated to the target polynucleotides in one or more mixtures of a total of 768 (3 x 256) members Optionally, an encoded adaptor may also comprise a spacer region, as shown m the above example where the 4 nucleotide sequence "ttct" serves as a spacer between the protrudmg strand and the oligonucleotide tag After hgation of the first set of encoded adaptors (28), (30), and (32), the tag- polynucleotide conjugates are cleaved (34) with the nuclease of cleavage adaptor A2, after which a second set of encoded adaptors is applied to form conjugates (36), (38), and (40) (Fig ID) Finally, the tag-polynucleotide conjugates are cleaved (42) with the nuclease of cleavage adaptor A3, after which a third set of encoded adaptors is applied to form conjugates (44), (46), and (48) (Fig IE) After completion of the succession of cleavages and hgations of encoded adaptors, the mixture is loaded (50) onto one or more solid phase supports via oligonucleotide tags t\ through t\. as desenbed more fully below, and as taught by Brenner, e g PCT/US95/12791 or PCT/US96/09513 If a single target polynucleotide is analyzed, then clearly multiple oligonucleotide tags, t j , t2, t^, are not necessary In such an embodiment, biotin, or like moiety, can be employed to anchor the polynucleotide-encoded adaptor conjugate, as no sorting is required Also, the ordering of the steps of cleavage, hgation, and loading onto solid phase supports depends on the particular embodiment implemented For example, the tag-polynucleotide conjugates may be loaded onto solid phase support first, followed by hgation of cleavage adaptors, cleavage thereof, and hgation of encoded adaptors, or, the cleavage adaptors may be ligated first, followed bv loadmg, cleavage, and hgation of encoded adaptors, and so on After encoded adaptors are ligated to the ends of a target polynucleotide in accordance with the invention, sequence information is obtained by successively applymg labeled tag complements to the immobilized target polynucleotides, either individually or as mixtures under conditions that permit the formation of perfectly matched duplexes and/or triplexes between the oligonucleotide tags of the encoded adaptors and their respective tag complements The numbers and complexity of the mixtures depends on several factors, including the type of labelmg system used, the length of the portions whose sequences are to be identifed, whether complexity reducing analogs are used, and the like Preferably, for the embodiment illustrated in Figures la through le, a single fluorescent dye is used to label each of 48 (=3 \ 16) tag complements The tag complements are applied individually to identify the nucleotides of each of the four-nucleotide portions of the target polynucleotide (1 e , 4 tag complements for each of 12 positions for a total of 48) Clearly, portions of different lengths would require different numbers of tag complements, e g in accordance with this embodiment, a 5-nucleotιde portion would require 20 tag complements, a 2-nucleotιde portion would require 8 tag complements, and so on The tag complements are applied under conditions sufficiently str gent so that only perfectly match duplexes are formed, signals from the fluorescent labels on the specifically hybridized tag complements are measured, and the tag complements are washed from the encoded tags so that the next mixture can be applied The 16 tag complements have a one-to-one correspondence with the following sequences of the 4-mer portions of the target sequence where "N" is any one of the nucleotides, A, C, G, or T Thus, for each nucleotide position four separate interrogations arc made, one for each kind of nucleotide This embodiment incorporates a significant degree of redundancy (a total of 16 tag complements are used to identify 4 nucleotide) in exchange for increased reliability of nucleotide determination Alternatively, 12 mixtures of 4 tag complements each could applied in succession by usmg four spectrally distinguishable fluorescent dyes, such that there is a one-to-one correspondence between dyes and kinds of nucleotide For example, a mixture of 4 tag complements may identify nucleotide "x" in the protruding strand sequence "nnxn" so that a first fluorescent label is observed if x=A, a second fluorescent label is observed if x=C, a third fluorescent label is observed if x=G, and so on Further sequence information can be obtained using the embodiment described above a process analogous to the "multi-steppmg" process disclosed in Brenner, International patent application PCT/US95/03678 (WO 95/27080) In this embodiment, a fourth adaptor, referred to herein as a "stepping adaptor," is ligated to the ends of the target polynucleotides along with cleavage adaptors Aj, A2, and A3, for example, in a concentration ratio of 3 1 1 1 Thus, approximately half of the available ends are ligated to the stepping adaptor The stepping adaptor includes a recognition site for a type Ils nuclease positioned such that its reach (defined below) will permit cleavage of the target polynucleotides at the end of the sequence determined via cleavage adaptors Aj, A2, and A3 An example of a stepping adaptor that could be used with the above set of cleavage adaptors is as follows NN ... NCTGGAGA cgannnnnnnnnnnnnnnnnnn ... -3 NN ... NGACCTCTGCp tnnnnnnnnnnnnnnnnnnn ... -5 ' where, as above, the recognition site of the nuclease, in this case BpM I, is singly underlined and the nucleotides at the cleavage site are doubly underlined The target polynucleotides cleaved with the nuclease of the stepping adaptor may be ligated to a further set of cleavage adaptors A4, A5, and Ag, which may contain nuclease recognition sites that are the same or different than those contained in cleavage adaptors A \ , A2, and A3 Whether or not an enlarged set of encoded adaptors is required depends on whether cleavage and hgation reactions can be tolerated in the signal measurement apparatus If, as above, it is desired to minimize enzyme reactions in connection with signal measurement, then additional sets of encoded adaptors must be employed That is, where above 768 oligonucleotide tags and tag complements were called for, with six cleavage reactions producmg protrudmg strands of four nucleotides each, 1536 oligonucleotide tags and tag complements (24 mixtures of 64 tag complements each) would be required Exemplary, cleavage adaptors A4, A5, and Ag, with the same nuclease recognition sites as A j , A2, and A3, and which could be used with the stepping adaptor shown above are as follows (4) nnnnnnnnnnnnnnnnnn ... -3 nnnnnnnnnnnnnnnnnnnn ... -5 (5) nnnnnnnnnnnnnnnnnn ... -3 nnnnnnnnnnnnnnnnnnnn ... -5 (6) nnnnnnnnnnnnnnnnnn ... -3' nnnnnnnnnnnnnnnnnnnn ... -5' where the cleavage sites are mdicated by double underlining Cleavage adaptors A4, A5, and Ag are preferably applied as mixtures, such that every possible two-nucleotidc protruding strand is represented Once the encoded adaptors have been ligated, the target polynucleotides are prepared for loading onto solid phase supports, preferably microparticles, as disclosed in Brenner, International patent application PCT/US95/ 12791 (WO 96/ 12041 ) Briefly, the oligonucleotide tags for sorting are rendered single stranded using a "stripping" reaction with T4 DNA polymerase, c g Kuijper et al (cited above) The single stranded oligonucleotide tags are specifically hybridized and ligated to their tag complements on microparticles The loaded microparticles are then analyzed m an instrument, such as described in Brenner (cited above) which permits the sequential delivery, specific hybridization, and removal of labeled tag complements to encoded adaptors In embodiments where encoded adaptors are ligated to a target polynucleotide (or population of target polynucleotides) only one time, there are several non-enzymatic template- driven methods of hgation that may used in accordance with the invention Such hgation methods include, but are not limited to, those disclosed in Shabarova, Biochimie 70 1323- 1334 (1988), Dohnnaya et al, Nucleic Acids Research, 16 3721-3738 (1988), Letsinger et al, U S patent 5,476,930, Gryaznov et al, Nucleic Acids Research, 22 2366-2369 (1994), Kang et al, Nucleic Acids Research, 23 2344-2345 (1995), Gryaznov et al, Nucleic Acids Research, 21 1403-1408 (1993), Gryaznov, U S patent 5,571,677, and like references Preferably, non-enzymatic hgation is carried out by the method of Letsinger et al (cited above) In this method, an encoded adaptor having a 3'-bromoacetylated end is reacted with a polynucleotide havmg a complementary protrudmg strand and a thiophosphoryl group at its 5' end An exemplary encoded adaptor employing such chemistry has the following structure BrCH 2 ( =0 ) CNH- ( B ) r ( B ) s ( B ) q ( B ) t -3 ' S ' -ZB ' B ' B ' B ' B ' ( B ' ) r ( B ' ) s ( B ' ) q -5 ' where B and B' are nucleotides and their complements, and z, r, s, q, and t are as described below Br, C, H, and N have their usual chemical meanings As explained in the above references, in a template-driven reaction, the 3'-bromacetylated oligonucleotide reacts spontaneously with an oligonucleotide having a 5'-thιophosphoryl group under aqueous conditions to form a thiophosphorylacetylammo linkage A thiophosphoryl group is readily attached to the 5' hydroxyl of a target polynucleotide by treatment with T4 kmasc in the presence of adenosιne-5'-0-(l-thιotπphosphate), I e g-S-ATP, as described in Kang ct al (cited above) Sequence Analysis with Cvcles of Ligation and Cleavage Encoded adaptors may be used in an adaptor-based method of DNA sequencing that mcludes repeated cycles of hgation, identification, and cleavage, such as the method described m Brenner, U S patent 5,599,675 and PCT Publication No WO 95/27080 Bncfly, such a method comprises the following steps (a) hgating an encoded adaptor to an end of a polynucleotide, the encoded adaptor having a nuclease recognition site of a nuclease whose cleavage site is separate from its recognition site, (b) identifying one or more nucleotides at the end of the polynucleotide by the identity of the encoded adaptor ligated thereto, (c) cleaving the polynucleotide with a nuclease recognizing the nuclease recognition' site of the encoded adaptor such that the polynucleotide is shortened by one or more nucleotides; and (d) repeating said steps (a) through (c) until said nucleotide sequence of the polynucleotide is determined In the identification step, successive sets of tag complements are specifically hybridized to the respective tags earned by encoded adaptors ligated to the ends of the target polynucleotides, as described above The type and sequence of nucleotides in the protruding strands of the polynucleotides are identified by the label carried by the specifically hybridized tag complement and the set from which the tag complement came, as described above Oligonucleotide Tags and Tag Complements Oligonucleotide tags are employed for two different purposes in the preferred embodiments of the invention Oligonucleotide tags are employed as described m Brenner, International patent applications PCT US95/12791 and PCT/US96/09513 (WO 96/12041 and WO 96/41011), to sort large numbers of polynucleotides, e g several thousand to several hundred thousand, from a mixture into umform populations of identical polynucleotides for analysis, and they are employed to deliver labels to encoded adaptors that number in the range of a few tens to a few thousand For the former use, large numbers, or repertoires, of tags are typically required, and therefore synthesis of individual oligonucleotide tags is problematic In these embodiments, combmatonal synthesis of the tags is preferred On the other hand, where extremely large repertoires of tags are not required—such as for delivering labels to encoded adaptors, oligonucleotide tags of a minimally cross-hybndizing set may be separately synthesized, as well as synthesized combinatoπally As descnbed in Brenner (cited above), the nucleotide sequences of oligonucleotides of a minimally cross-hybndizing set are conveniently enumerated by simple computer programs, such as those exemplified by the programs whose source codes are listed m Appendices I and II Similar computer programs arc readily written for listing oligonucleotides of minimally cross-hybndizing sets for any embodiment of the invention Table I below provides guidance as to the size of sets of minimally cross-hybndizing oligonucleotides for the indicated lengths and number of nucleotide differences The above computer programs were used to generate the numbers Sets containing several hundred to several thousands, or even several tens of thousands, of oligonucleotides may be synthesized directly by a vanety of parallel synthesis approaches, e g as disclosed in Frank et al, U S patent 4,689,405, Frank et al, Nucleic Acids Research, 1 1 4365-4377 (1983), Matson et al, Anal Biochem , 224 1 10-1 16 (1995), Fodor et al, International application PCT US93/04145 (WO 93/22684), Pease et al, Proc Natl Acad Sci , 91 5022-5026 (1994), Southern et al, J Biotechnology, 35 217-227 (1994), Brennan, International application PCT/US94/05896 (WO 94/27719), Lashkan et al, Proc Natl Acad Sci , 92 7912-7915 (1995), or the like Preferably, tag complements in mixtures, whether synthesized combinatonally or individually, are selected to have similar duplex or tnplex stabilities to one another so that perfectly matched hybnds have similar or substantially identical melting temperatures This permits mis-matched tag complements to be more readily distinguished from perfectly matched tag complements when applied to encoded adaptors, e g by washing under stringent conditions For combinatonally synthesized tag complements, mmimally cross-hybndizing sets may be constructed from subumts that make approximately equivalent contπbutions to duplex stability as every other subunit m the set Guidance for carrying out such selections is provided by published techniques for selecting optimal PCR primers and calculating duplex stabilities, e g Rychhk et al, Nucleic Acids Research, 17 8543-8551 (1989) and 18 6409- 6412 (1990), Breslauer et al, Proc Natl Acad Sci , 83 3746-3750 (1986), Wetmur, Cnt Rev Biochem Mol Biol , 26 227-259 (1991), and the like When smaller numbers of oligonucleotide tags are required, such as for delivering labels to encoded adaptors, the computer programs of Appendices I and II may be used to generate and list the sequences of mmimally cross-hybndizing sets of oligonucleotides that are used directly (I e without concatenation into "sentences") Such lists can be further screened for additional cntena, such as GC-content, distribution of mismatches, theoretical melting temperature, and the like, to form additional minimally cross-hybndizing sets For shorter tags, e g about 30 nucleotides or less, the algonthm described by Rychhk and Wetmur is preferred for calculating duplex stability, and for longer tags, e g about 30-35 nucleotides or greater, an algonthm disclosed by Suggs et al, pages 683-693 in Brown, editor, ICN-UCLA Symp Dev Biol , Vol 23 (Academic Press, New York, 1981) may be conveniently employed Clearly, there are many approaches available to one skilled in the art for designing sets of minimally cross-hybndizing subumts within the scope of the invention For example, to minimize the affects of different base-stacking energies of terminal nucleotides when subumts are assembled, subu ts may be provided that have the same terminal nucleotides In this way, when subumts are linked, the sum of the base-stacking energies of all the adjoining terminal nucleotides will be the same, thereby reducing or eliminating variability m tag melting temperatures In multi-subunit tags, a "word" of terminal nucleotides, shown in italic below, may also be added to each end of a tag so that a perfect match is always formed between it and a similar terminal "word" on any other tag complement Such an augmented tag would have the form where the primed W's indicate complements With ends of tags always forming perfectly matched duplexes, all mismatched words will be internal mismatches thereby reducing the stability of tag-complement duplexes that otherwise would have mismatched words at their ends It is well known that duplexes with internal mismatches are significantly less stable than duplexes with the same mismatch at a terminus With oligonucleotide tags used for sorting, a preferred embodiment of minimally cross-hybndizing sets are those whose subumts are made up of three of the four natural nucleotides As will be discussed more fully below, the absence of one type of nucleotide in the oligonucleotide tags permits target polynucleotides to be loaded onto solid phase supports by use of the 5'— »3' exonuclease activity of a DNA polymerase The following is an exemplary mmimally cross-hybπdizmg set of subumts each comprising four nucleotides selected from the group consisting of A, G, and T Table II Word w 5 w 6 w 7 Wg Sequence : GTAA AGT A ATGT AAAG In this set, each member would form a duplex having three mismatched bases with the complement of every other member With oligonucleotide tags used for delivering labels to encoded adaptors, all four nucleotides are employed The oligonucleotide tags of the invention and their complements are conveniently synthesized on an automated DNA synthesizer, e g an Applied Biosystems, Inc (Foster City, California) model 392 or 394 DNA/RNA Synthesizer, using standard chemistnes, such as phosphoramiditc chemistry, c g disclosed in the following references Beaucage and Iyer, Tetrahedron, 48 2223-2311 (1992), Molko et al, U S patent 4,980,460, Koster et al, U S patent 4,725,677, Caruthers et al, U S patents 4,415,732, 4,458,066, and 4,973,679, and the like Alternative chemistnes, e g resulting m non-natural backbone groups, such as peptide nucleic acids (PNAs), N3'— >P5' phosphorami dates, and the like, may also be employed In some embodiments, tags may comprise naturally occurnng nucleotides that permit processmg or manipulation by enzymes, while the corresponding tag complements may compnse non- natural nucleotide analogs, such as peptide nucleic acids, or like compounds, that promote the formation of more stable duplexes during sorting In the case of tags used for de veπng label to encoded adaptors both the oligonucleotide tags and tag complements may be constructed from non-natural nucleotides, or analogs, provided hgation can take place, either chemically or enzymatically Double stranded forms of tags may be made by separately synthesizing the complementary strands followed by mixing under conditions that permit duplex formation Alternatively, double stranded tags may be formed by first synthesizing a smgle stranded repertoire linked to a known oligonucleotide sequence that serves as a primer binding site The second strand is then synthesized by combining the single stranded repertoire with a primer and extending with a polymerase This latter approach is described in O phant et al, Gene, 44 177-183 (1986) Such duplex tags may then be inserted into cloning vectors along with target polynucleotides for sorting and manipulation of the target polynucleotide m accordance with the mvention When tag complements are employed that are made up of nucleotides that have enhanced bmding charactenstics, such as PNAs or oligonucleotide N3'— »P5' phosphoramidates, sorting can be implemented through the formation of D-loops between tags comprising natural nucleotides and their PNA or phosphoramidate complements, as an alternative to the "stnpping" reaction employing the 3'— »5' exonuclcase activity of a DNA polymerase to render a tag smgle stranded Oligonucleotide tags for sorting may range in length from 12 to 60 nucleotides or basepairs Preferably, oligonucleotide tags range in length from 18 to 40 nucleotides or basepairs More preferably, oligonucleotide tags range in length from 25 to 40 nucleotides or basepairs In terms of preferred and more preferred numbers of subumts, these ranges may be expressed as follows Table III Numbers of Subumts m Tags in Preferred Embodiments Monomers in Subunit Nucleotides in Oligonucleotide Tag (12-60) (18-40) (25-40) 3 4-20 subumts 6-13 subumts 8-13 subumts 4 3-15 subumts 4-10 subumts 6-10 subumts 5 2-12 subumts 3-8 subumts 5-8 subumts 6 2-10 subumts 3-6 subumts 4-6 subumts Most preferably, oligonucleotide tags for sorting are single stranded and specific hybndization occurs via Watson-Cnck pairing with a tag complement Preferably, repertoires of smgle stranded oligonucleotide tags for sorting contain at least 100 members, more preferably, repertoires of such tags contain at least 1000 members, and most preferably, repertoires of such tags contain at least 10,000 members Preferably, repertoires of tag complements for de veπng labels contain at least 16 members, more preferably, repertoires of such tags contain at least 64 members Still more preferably, such repertoires of tag complements contain from 16 to 1024 members, e g a number for identifying nucleotides in protruding strands of from 2 to 5 nucleotides in length Most preferably, such repertoires of tag complements contain from 64 to 256 members Repertoires of desired sizes are selected by directly generating sets of words, or subumts, of the desired size, e g with the help of the computer programs of Appendices I and II, or repertoires are formed generating a set of words which arc then used in a combinatoπal synthesis scheme to give a repertoire of the desired size Preferably, the length of smgle stranded tag complements for dehvermg labels is between 8 and 20 More preferably, the length is between 9 and 15 Tnplex Tags In embodiments where specific hybndization occurs via triplex formation, coding of tag sequences follows the same principles as for duplex-forming tags, however, there are further constraints on the selection of subunit sequences Generally, third strand association via Hoogsteen type of binding is most stable along homopynmidine-homopunne tracks in a double stranded target Usually, base triplets form in T-A*T or C-G*C motifs (where "-" indicates Watson-Cnck pairmg and "*" indicates Hoogsteen type of binding), however, other motifs are also possible For example, Hoogsteen base pairing permits parallel and antiparallel onentations between the third strand (the Hoogsteen strand) and the punne-nch strand of the duplex to which the third strand binds, depending on conditions and the composition of the strands There is extensive guidance m the literature for selecting appropriate sequences, orientation, conditions, nucleoside type (e g whether nbose or deoxynbose nucleosides are employed), base modifications (e g methylated cytosine, and the like) m order to maximize, or otherwise regulate, tnplex stability as desired in particular embodiments, e g Roberts et al, Proc Natl Acad Sci , 88 9397-9401 (1991), Roberts et al, Science, 258 1463-1466 (1992), Roberts et al, Proc Natl Acad Sci , 93 4320-4325 (1996), Distefano et al, Proc Natl Acad Sci , 90 1179-1183 (1993), Mergny et al, Biochemistry, 30 9791-9798 (1991), Cheng et al, J Am Chem Soc , 1 14 4465-4474 (1992), Beal and Dervan, Nucleic Acids Research, 20 2773-2776 (1992), Beal and Dervan, J Am Chem Soc , 114 4976-4982 (1992), Giovannange et al, Proc Natl Acad Sci , 89 8631-8635 (1992), Moser and Dervan, Science, 238 645-650 (1987), McShan et al, J Biol Chem , 267 5712-5721 (1992), Yoon et al, Proc Natl Acad Sc , 89 3840-3844 (1992), Blume et al, Nucleic Acids Research, 20 1777-1784 (1992), Thuong and Helene, Angew Chem Int Ed Engl 32 666-690 (1993), Escude et al, Proc Natl Acad Sci , 93 4365-4369 (1996), and the like Conditions for annealmg smgle-stranded or duplex tags to their single- stranded or duplex complements are well known, e g Ji et al, Anal Chem 65 1323-1328 (1993), Cantor et al, U S patent 5,482,836, and the like Use of triplex tags m sorting has the advantage of not requinng a "stπppmg" reaction with polymerase to expose the tag for annealing to its complement Preferably, oligonucleotide tags of the mvention employing triplex hybndization are double stranded DNA and the corresponding tag complements are single stranded More preferably, 5-methylcytosιne is used m place of cytosine m the tag complements in order to broaden the range of pH stability of the triplex formed between a tag and its complement Preferred conditions for forming triplexes are fully disclosed in the above references Briefly, hybridization takes place m concentrated salt solution, e g 1 0 M NaCl, 1 0 M potassium acetate, or the like, at pH below 5 5 ( or 6 5 if 5-methylcytosme is employed) Hybridization temperature depends on the length and composition of the tag, however, for an 18-20-mer tag or longer, hybridization at room temperature is adequate Washes may be conducted with less concentrated salt solutions, e g 10 mM sodium acetate, 100 mM MgCl2, pH 5 8, at room temperature Tags may be eluted from their tag complements by mcubation m a similar salt solution at pH 9 0 Minimally cross-hybndizing sets of oligonucleotide tags that form triplexes may be generated by the computer program of Appendix II, or similar programs An exemplary set of double stranded 8-mer words are listed below in capital letters with the corresponding complements in small letters Each such word differs from each of the other words in the set by three base pairs Table IV Exemplary Minimally Cross-Hybndizmg Set of DoubleStranded 8-mer Tags 5'-AAGGAGAG 5' -AAAGGGGA 5' -AGAGAAGA 5'-AGGGGGGG 3'-TTCCTCTC 3'-TTTCCCCT 3'-TCTCTTCT 3'-TCCCCCCC 3'-ttcctctc 3' -tttcccct 3'-tctcttct 3'-tccccccc 5'-AAAAAAAA 5' -AAGAGAGA 5' -AGGAAAAG 5' -GAAAGGAG 3'-TTCTCTCT 3'-TCCTTTTC 3' -CTTTCCTC 3'-tttttttt 3' -ttctctct 3'-t_ccttttc 3'-ctttcctc 5'-AAAAAGGG 5' -AGAAGAGG 5' -AGGAAGGA 5' -GAAGAAGG 3'-TTTTTCCC 3' -TCTTCTCC 3'-TCCTTCCT 3'-CTTCTTCC 3'-tttttccc 3' -tcttctcc 3' -tccttcct 3' -cttcttcc 5'-AAAGGAAG 5' -AGAAGGAA 5' -AGGGGAAA 5' -GAAGAGAA 3' -TTTCCTTC 3' -TCTTCCTT 3'-TCCCCTTT 3' -CTTCTCTT 3'-tttccttc 3' -tcttcctt 3' -tccccttt 3'-cttctctt Table V Repertoire Size of Various Double Stranded Tags That Form Tn lexes with Their Ta Com lements Synthesis and Structure of Adaptors The encoded adaptors and cleavage adaptors are conveniently synthesized on automated DNA synthesizers using standard chemistnes, such as phosphoramidite chemistry, e g disclosed in the following references Beaucage and Iyer, Tetrahedron, 48 2223-231 1 (1992), Molko et al, U S patent 4,980,460, Koster et al, U S patent 4,725,677, Caruthers et al, U S patents 4,415,732, 4,458,066, and 4,973,679, and the like Alternative chemistries, e g resultmg in non-natural backbone groups, such as phosphorothioate, phosphoramidate, and the like, may also be employed provided that the resulting oligonucleotides are compatible with the hgation and/or cleavage reagents used in a particular embodiment Typically, after synthesis of complementary strands, the strands are combined to form a double stranded adaptor The protruding strand of an encoded adaptor may be synthesized as a mixture, such that every possible sequence is represented m the protruding portion Such mixtures are readily synthesized using well known techniques, e g as disclosed in Telenius et al, Genomics, 13 718-725 (1992), Welsh et al, Nucleic Acids Research, 19 5275-5279 (1991), Grothues et al, Nucleic Acids Research, 21 1321-1322 (1993), Hartley, European patent application 90304496 4 (EP Publication No 395398), and the like Generally, these techniques simply call for the application of mixtures of the activated monomers to the growing oligonucleotide during the coupling steps where one desires to introduce multiple nucleotides As discussed above, in some embodiments it may be desirable to reduce the complexity of the adaptors This can be accomplished using complexity reducing analogs, such as deoxymosine, 2-ammopunne, or the like, e g as taught in Kong Thoo Lin et al, Nucleic Acids Research, 20 5149-5152, or by U S patent 5,002,867, Nichols et al, Nature, 369 492-493 (1994), and the like In some embodiments, it may be desirable to synthesize encoded adaptors or cleavage adaptors as a single polynucleotide which contains self-complementary regions After synthesis, the self-complementary regions are allowed to anneal to form a adaptor with a protruding strand at one end and a single stranded loop at the other end Preferably, in such embodiments the loop region may comprise from about 3 to 10 nucleotides, or other comparable linking moieties, e g alkylethcr groups, such as disclosed in U S patent 4,914,210 Many techniques are available for attaching reactive groups to the bases or internucleoside linkages for labelmg, as discussed in the references cited below When conventional gases are employed in the invention, as described more fully below, the 5' end of the adaptor may be phosphorylated in some embodiments A 5' monophosphate can be attached to a second oligonucleotide either chemically or enzymatically with a kinase, e g Sambrook et al, Molecular Cloning A Laboratory Manual, 2nd Edition (Cold Spring Harbor Laboratory, New York, 1989) Chemical phosphorylation is described by Horn and Urdea, Tetrahedron Lett , 27 4705 (1986), and reagents for carrying out the disclosed protocols are commercially available, e g 5' Phosphate-ON τ M from Clontcch Laboratories (Palo Alto, California) Encoded adaptors of the invention can have several embodiments depending, for example, on whether single or double stranded tags are used, whether multiple tags are used, whether a 5' protruding strand or 3' protruding strand is employed, whether a 3' blocking group is used, and the like Formulas for several embodiments of encoded adaptors are shown below Preferred structures for encoded adaptors us g one single stranded tag are as follows- -p(N) n (N ) r (N ) S (N )_(N ) t -3' z(N') r (N') s (N' ) q -5' or p(N ) r (N ) S {N ) (N ) t -3' 3'-z(N) n (N' ) r (N') s (N' ) q -5' where N is a nucleotide and N' is its complement, p is a phosphate group, z is a 3' hydroxyl or a 3' blocking group, n is an mteger between 2 and 6, inclusive, r is an integer greater than or equal to 0, s is an mteger which is cither between four and six whenever the encoded adaptor has a nuclease recognition site or is 0 whenever there is no nuclease recognition site, q is an integer greater than or equal to 0, and t is an integer between 8 and 20, inclusive More preferably, n is 4 or 5, and t is between 9 and 15, inclusive Whenever an encoded adaptor contains a nuclease recogmtion site, the region of "r" nucleotide pairs is selected so that a predetermined number of nucleotides are cleaved from a target polynucleotide whenever the nuclease recognizing the site is applied The size of "r" in a particular embodiment depends on the reach of the nuclease (as the term is defined in U S patent 5,599,675 and WO 95/27080) and the number of nucleotides sought to be cleaved from the target polynucleotide Preferably, r is between 0 and 20, more preferably, r is between 0 and 12 The region of "q" nucleotide pairs is a spacer segment between the nuclease recognition site and the tag region of the encoded probe The region of "q" nucleotide may include further nuclease recognition sites, labelling or signal generating moieties, or the like The single stranded oligonucleotide of "t" nucleotides is a "t-mer" oligonucleotide tag selected from a minimally cross-hybndizing set The 3' blocking group "z" may have a variety of forms and may include almost any chemical entity that precludes hgation and that does not interfere with other steps of the method, e g removal of the 3' blocked strand, hgation, or the like Exemplary 3' blocking groups include, but are not limited to, hydrogen (I e 3' deoxy), phosphate, phosphorothioate, acetyl, and the like Preferably, the 3' blocking group is a phosphate because of the convenience in adding the group during the synthesis of the 3' blocked strand and the convenience in removing the group with a phosphatase to render the strand capable of ligation with a ligase. An oligonucleotide having a 3' phosphate may be synthesized using the protocol described in chapter 12 of Eckstein, Editor, Oligonucleotides and Analogues: A Practical Approach (IRL Press, Oxford, 1991 ). Further 3' blocking groups are available from the chemistries developed for reversable chain terminating nucleotides in base-by-base sequencing schemes, e.g. disclosed in the following references: Cheeseman, U.S. patent 5,302,509; Tsien et al, International application WO 91/06678; Canard et al, Gene, 148: 1-6 (1994); and Metzker et al, Nucleic Acids Research, 22: 4259-4267 (1994). Roughly, these chemistries permit the chemical or enzymatic removal of specific blocking groups (usually having an appendent label) to generative a free hydroxyl at the 3' end of a priming strand. Preferably, when z is a 3' blocking group, it is a phosphate group and the double stranded portion of the adaptors contain a nuclease recognition site of a nuclease whose recognition site is separate from its cleavage site. When double stranded oligonucleotide tags are employed that specifically hybridize with single stranded tag complements to form triplex structures, encoded tags of the invention preferably have the following form: 5'-p(N) n (N ) r (N ) S (N (N .-3' z(N*) r (N') s (N') q (N' _-5 or p(N ) r (N ) S (N ) q (N ) t -3' 3'-z(N) n (N') r (N') s (N') q (N' ) t -5' where N, N', p, q, r, s, z, and n are defined as above. Preferably, in this embodiment t is an integer in the range of 12 to 24. Clearly, there are additional structures which contain elements of the basic designs set forth above that would be apparent to those with skill in the art. For example, encoded adaptors of the invention include embodiments with multiple tags, such as the following: 5'-p(N) n (N ) r (N ) S (N ) (N ) tl (N ) t k" 3 ' z(N') r (N') s (N') q (N')tl ... ( N ') k- 5 or p(N ) r (N ) S (N ) (N ) tl ... (N ) tk -3 3'-z(N) n (N , ) r (N') s (N') q (N') t l ... (N') tk -5' where the encoded adaptor includes k double stranded tags Preferably, t|=t2— tfc and k is either 1, 2, or 3 Labeling Tag Complements The tag complements of the invention can be labeled in a vanety of ways for decodmg oligonucleotide tag, including the direct or indirect attachment of radioactive moieties, fluorescent moieties, coloπmetnc moieties, chemiluminescent moieties, and the like Many comprehensive reviews of methodologies for labeling DNA and constructing DNA adaptors provide guidance applicable to constructing adaptors of the present invention Such reviews include Matthews et al, Anal Biochem . Vol 169, pgs 1-25 (1988), Haugland, Handbook of Fluorescent Probes and Research Chemicals (Molecular Probes, Inc , Eugene, 1992), Keller and Manak, DNA Probes, 2nd Edition (Stockton Press, New York, 1993), and Eckstem, editor, Oligonucleotides and Analogues A Practical Approach (IRL Press, Oxford, 1991), Wetmur, Critical Reviews in Biochemistry and Molecular Biology, 26 227-259 (1991), and the like Many more particular methodologies applicable to the invention are disclosed in the following sample of references Fung et al, U S patent 4,757, 141, Hobbs, Jr , et al U S patent 5,151,507, Cruickshank, U S patent 5,091,519, (synthesis of functiona zed oligonucleotides for attachment of reporter groups), Jablonski et al Nucleic Acids Research, 14 61 15-6128 (1986)(enzyme-ohgonucleotιde conjugates), Ju et al, Nature Medicine, 2 246- 249 ( 1996), and Urdca et al, U S patent 5 , 124,246 (branched DNA) Attachment sites of labeling moieties are not critical, provided that such labels do not interfere with the hgation and/or cleavage steps Preferably, one or more fluorescent dyes are used as labels for tag complements, e g as disclosed by Menchen et al, U S patent 5, 188,934, Bergot et al PCT application PCT/US90/05565 (WO 91/05060) As used herein, the term "fluorescent signal generating moiety" means a signaling means which conveys information through the fluorescent absorption and/or emission properties of one or more molecules Such fluorescent properties mclude fluorescence intensity, fluorescence life time, emission spectrum characteristics, energy transfer, and the like Ligating Adaptors and Preventing Self-Ligation In accordance with the preferred embodiment of th invention, cleavage adaptors are ligated to the ends of target polynucleotides to prepare such ends for eventual hgation of encoded adaptors Preferably, hgation is carried out enzymatically using a hgase in a standard protocol Many gases are known and arc suitable for use in the invention, e g Lehman, Science, 186 790-797 (1974), Engler et al, DNA Ligases, pages 3-30 m Boyer, editor, The Enzymes, Vol 15B (Academic Press, New York, 1982), and the like Preferred gases include T4 DNA gase, T7 DNA hgase, E coli DNA hgase, Taq gase, Pfu gase, and Tth gase Protocols for their use are well known, e g Sambrook et al (cited above), Barany, PCR Methods and Applications, 1 5-16 (1991), Marsh et al, Strategies, 5 73-76 (1992), and the like Generally, hgases require that a 5' phosphate group be present for hgation to the 3' hydroxyl of an abuttmg strand This is conveniently provided for at least one strand of the target polynucleotide by selectmg a nuclease which leaves a 5' phosphate, e g as Fok l A special problem may arise in dealmg with either polynucleotide ends or adaptors that are capable of self-hgation, such as illustrated in Figure 2, where the four-nucleotide protrudmg strands of the anchored polynucleotides are complementary to one another (114) This problem is especially severe m embodiments where the polynucleotides (112) to be analyzed are presented to the adaptors as umform populations of identical polynucleotides attached to a solid phase support (110) In these situations, the free ends of the anchored polynucleotides can twist around to form perfectly matched duplexes (1 16) with one another If the 5' strands of the ends are phosphorylated, the polynucleotides are readily ligated in the presence of a hgase An analogous problem also exists for double stranded adaptors Namely, whenever their 5' strands are phosphorylated, the 5' strand of one adaptor may be ligated to the free 3' hydroxyl of another adaptor whenever the nucleotide sequences of their protruding strands are complementary When self-hgation occurs, the protruding strands of neither the adaptors nor the target polynucleotides are available for analysis or processing This, in turn, leads to the loss or disappearance of signals generated in response to correct hgations of adaptors to target polynucleotides Since the probability of a pahndromic 4-mer occurring in a random sequence is the same as the probability of a repeated pair of nucleotides (6 25%), adaptor-based methods for de novo sequencing have a high expectation of failure after a few cycles because of self-hgation When this occurs, further analysis of the polynucleotide becomes impossible The above problems may be addressed by implementing the invention in the following steps, which are illustrated in Figure 3 A for a preferred embodiment (a) hgating (120) an encoded adaptor to an end of the polynucleotide (122), where the end of the polynucleotide has a dephosphorylated 5' hydroxyl, and the end of the encoded adaptor (124) to be ligated has a first strand (126) and a second strand (128), and the second strand of the encoded adaptor has a 3' blocking group (130), (b) removing the 3' blocking group of the second strand after hgation, e g by washmg (132), or by enzymatically or chemically removing the group in situ, e g by treatment with a phosphatase if the blocking group is a phosphate, (c) phosphorylatmg (134) the 5' hydroxyl of the polynucleotide, (d) hgating (136) a second strand (142) having an unblocked 3' moiety to regenerate the encoded adaptor (138), and (e) identifying (144) one or more nucleotides at the end of the polynucleotide by the identity of the encoded adaptor ligated thereto, e g via a fluorescently labelled (140) tag complement The encoded adaptors and target polynucleotides may be combined for hgation either singly or as mixtures For example, a single kind of adaptor having a defined sequence may be combined with a smgle kind of polynucleotide havmg a common (and perhaps, unknown) nucleotide sequence, or a single kmd of adaptor havmg a defined sequence may be combined with a mixture of polynucleotides, such as a plurality of umform populations of identical polynucleotides attached to different solid phase supports in the same reaction vessel, e g described by Brenner et al, International application PCT/US96/09513 (WO 96/41011), or a mixture of encoded adaptors, particularly mixtures havmg different nucleotide sequences ln their protruding strands, may be combined with a single kind of polynucleotide, or a mixture of encoded adaptors may be combined with a mixture of polynucleotides When the term "adaptor", or "encoded adaptor," is used in the singular, it is meant to encompass mixtures of adaptors having different sequences of protruding strands as well as a single kind of adaptor having the same sequence of protruding strand, in a manner analogous to the usage of the term "probe " Besides removing by meltmg, a 3' deoxy may be removed from a second strand by a polymerase "exchange" reaction disclosed in Kuijper et al, Gene, 1 12 147-155 (1992), Aslarudis et al, Nucleic Acids Research, 18 6069-6074 (1990), and like references Briefly, the 5'— >3' exonuclease activity of T4 DNA polymerase, and like enzymes, may be used to exchange nucleotides in a priming strand with their tπphosphatc counterparts in solution, c g Kuijper et al (cited above) Thus, with such a reaction a 3' dideoxynucleotide can be exchanged with a 2'-deo\y-3'-hydroxynucleotιde from a reaction mixture, which renders the second strand hgatable to the target polynucleotide after treatment with a polynucleotide kinase A preferred embodiment employing cycles of hgation and cleavage comprises the following steps (a) hgating (220) an encoded adaptor to an end of the polynucleotide (222), the end of the polynucleotide having a dephosphorylated 5' hydroxyl, the end of the double stranded adaptor to be ligated (224) having a first strand (226) and a second strand (228), the second strand of the double stranded adaptor having a 3' blocking group (230), and the double stranded adaptor havmg a nuclease recognition site (250) of a nuclease whose recognition site is separate from its cleavage site, (b) removing the 3' blocking group after hgation, e g by washing off the second strand (232), (c) phosphorylatmg (234) the 5' hydroxyl of the polynucleotide, (d) hgating (236) a second strand (242) having an unblocked 3' moiety to regenerate the double stranded adaptor (238) and the nuclease recognition site (250), (e) identifying (244) one or more nucleotides at the end of the polynucleotide by the identity of the adaptor ligated thereto, (f) cleaving (252) the polynucleotide with a nuclease that recognizes the recogmtion site, such that the polynucleotide is shortened by one or more nucleotides, the recogmtion site bemg positioned m the illustrated adaptor (224) so that the cleavage (254) removes two nucleotides from polynucleotide (222), (g) dephosphorylatmg (256) the 5' end of the polynucleotide, and (h) repeatmg (258) steps (a) through (g) Typically, prior to hgation, ends of polynucleotides to be analyzed are prepared by digesting them with one or more restnction endonucleases that produce predetermined cleavages, usually havmg 3' or 5' protruding strands, 1 c "sticky" ends Such digestions usually leave the 5' strands phosphorylated Preferably, these 5' phosphorylated ends are dephosphorylated by treatment with a phosphatase, such as calf intestinal alkaline phosphatase, or like enzyme, using standard protocols, e g as descnbed in Sambrook et al, Molecular Cloning, Second Edition (Cold Spring Harbor Laboratory, New York, 1989) By removal of the 5' phosphates the target polynucleotides are rendered incapable of bemg ligated in the presence of a hgase The step of dephosphorylatmg preferably leaves a free 5* hydroxyl Preferred Nucleases "Nuclease" as the term is used m accordance with the invention means any enzyme, combination of enzymes, or other chemical reagents, or combinations chemical reagents and enzymes that when applied to a ligated complex, discussed more fully below, cleaves the ligated complex to produce an augmented adaptor and a shortened target polynucleotide A nuclease of the invention need not be a single protein, or consist solely of a combmation of proteins A key feature of the nuclease, or of the combination of reagents employed as a nuclease, is that its (their) cleavage site be separate from its (their) recognition site The distance between the recognition site of a nuclease and its cleavage site will be referred to herein as its "reach " By convention, "reach" is defined by two integers which give the number of nucleotides between the recognition site and the hydrolyzed phosphodiester bonds of each strand For example, the recognition and cleavage properties of Fok 1 is typically represented as "GGATG(9/13)" because it recognizes and cuts a double stranded DNA as follows (SEQ ID NO 2) 5 ' -... NNGGATGNNNNNNNNN NNNNNNNNNN ... 3 '-... NNCCTACNNNNNNNNNNNNN NNNNNN ... where the bolded nucleotides are Fok I's recognition site and the N's are arbitrary nucleotides and their complements It is important that the nuclease only cleave the target polynucleotide after it forms a complex with its recognition site, and preferably, the nuclease leaves a protruding strand on the target polynucleotide after cleavage Preferably, nucleases employed in the invention are natural protein endonucleases (I) whose recognition site is separate from its cleavage site and (n) whose cleavage results in a protruding strand on the target polynucleotide Most preferably, class Ils restriction endonucleases are employed as nucleases in the invention, e g as described m Szybalski et al, Gene, 100 13-26 (1991), Roberts et al, Nucleic Acids Research, 21 3125-3137 (1993), and Livak and Brenner, U S patent 5,093,245 Exemplary class Ils nucleases for use with the invention include Alw XI, Bsm Al, Bbv I, Bsm FI, Sts I, Hga I, Bsc Al, Bbv II, Bee fl, Bee 851, Bcc I, Beg I, Bsa I, Bsg I, Bsp MI, Bst 71 I, Ear I, Eco 571, Esp 31, Fau I, Fok I, Gsu I, Hph I, Mbo II, Mme I, Rle Al, Sap I, Sfa NI, Taq II, Tth 1 1 III, Bco 51, Bpu Al, Fin I, Bsr DI, and isoschizomers thereof Preferred nucleases include Bbv I, Fok I, Hga I, Ear I, and Sfa NI Bbv I is the most prefened nuclease Preferably, prior to nuclease cleavage steps, usually at the start of a sequencmg operation, the target polynucleotide is treated to block the recognition sites and/or cleavage sites of the nuclease being employed This prevents undesired cleavage of the target polynucleotide because of the fortuitous occuπence of nuclease recognition sites at intenor locations in the target polynucleotide Blocking can be achieved m a vaπety of ways, including methylation and treatment by sequence-specific aptamcrs, DNA binding protems, or oligonucleotides that form tnplexes Whenever natural protein endonucleases are employed, recognition sites can be convemently blocked by methylating the target polynucleotide with the cognate methylase of the nuclease being used That is, for most if not all type II bacterial restnction endonucleases, there exists a so-called "cognate" methylases that methylates its recognition site Many such methylases are disclosed in Roberts et al (cited above) and Nelson et al, Nucleic Acids Research, 21 3139-3154 (1993), and arc commercially available from a variety of sources, particularly New England Biolabs (Beverly, MA) Alternatively, if a PCR step is employed in preparing target polynucleotides for sequencing, 5-methylcytosιne tπphosphates may be used dunng amplification so that the natural cytosine are replaced by methylated cytosines m the amphcon This later approach has the added advantage of eliminating the need to treat a target polynucleotide bound to a solid phase support with another enzyme Clearly, one of ordinary skill in the art could combine features of the embodiments set forth above to design still further embodiments in accordance with the mvention, but not expressly set forth above A variety of kits are provided for carrying out different embodiments of the invention Generally, kits of the mvention mclude encoded adaptors, cleavage adaptors, and labeled tag complements Kits further include the nuclease reagents, the hgation reagents, and instructions for practicing the particular embodiment of the invention In embodiments employing natural protein endonucleases and hgases, hgase buffers and nuclease buffers may be included In some cases, these buffers may be identical Such kits may also include a methylase and its reaction buffer Preferably, kits also mclude one or more solid phase supports, e g microparticles carrying tag complements for sorting and anchoring target polynucleotides Attaching Tags to Polynucleotides For Sorting onto Solid Phase Supports An important aspect of the invention is the sorting and attachment of a populations of polynucleotides, e g from a cDNA library, to microparticles or to separate regions on a solid phase support such that each microparticle or region has substantially only one kind of polynucleotide attached This objective is accomplished by insunng that substantially all different polynucleotides have different tags attached This condition, in turn, is brought about by taking a sample of the full ensemble of tag-polynucleotide conjugates for analysis (It is acceptable that identical polynucleotides have different tags, as it merely results in the same polynucleotide being operated on or analyzed twice in two different locations ) Such sampling can be carried out either overtly— for example, by taking a small volume from a larger mixture—after the tags have been attached to the polynucleotides, it can be carried out inherently as a secondary effect of the techniques used to process the polynucleotides and tags, or sampling can be earned out both overtly and as an inherent part of processmg steps Preferably, in constructing a cDNA library where substantially all different cDNAs have different tags, a tag repertoire is employed whose complexity, or number of distinct tags, greatly exceeds the total number of RNAs extracted from a cell or tissue sample Preferably, the complexity of the tag repertoire is at least 10 times that of the polynucleotide population, and more preferably, the complexity of the tag repertoire is at least 100 times that of the polynucleotide population Below, a protocol is disclosed for cDNA library construction using a primer mixture that contains a full repertoire of exemplary 9-word tags 9 8 Such a mixture of tag-contaming primers has a complexity of 8 , or about 1 34 x 10 As indicated by Wmslow et al, Nucleic Acids Research, 19 3251-3253 (1991), mRNA for library construction can be extracted from as few as 10-100 mammalian cells Since a smgle 5 4 mammalian cell contains about 5 x 10 copies of mRNA molecules of about 3 4 x 10 different kinds, by standard techniques one can isolate the mRNA from about 100 cells, or 7 (theoretically) about 5 x 10 mRNA molecules Comparing this number to the complexity of the pnmer mixture shows that without any additional steps, and even assuming that mRNAs are converted into cDNAs with perfect efficiency (1% efficiency or less is more accurate), the cDNA library construction protocol results in a population containing no more than 37% of the total number of different tags That is, without any overt sampling step at all, the protocol inherently generates a sample that comprises 37%, or less, of the tag repertoire The probability of obtaining a double under these conditions is about 5%, which is within the preferred range With mRNA from 10 cells, the fraction of the tag repertoire sampled is reduced to only 3 7%, even assuming that all the processing steps take place at 100% efficiency In fact, the efficiencies of the processing steps for constructing cDNA libraπes are very low, a "rule of thumb" bemg that good library should contain about 10 cDNA clones from mRNA extracted from 10 mammalian cells Use of larger amounts of mRNA m the above protocol, or for larger amounts of polynucleotides in general, where the number of such molecules exceeds the complexity of the tag repertoire, a tag-polynucleotide conjugate mixture potentially contains every possible pairmg of tags and types of mRNA or polynucleotide. In such cases, overt sampling may be implemented by removing a sample volume after a senal dilution of the starting mixture of tag-polynucleotide conjugates The amount of dilution required depends on the amount of starting material and the efficiencies of the processing steps, which are readily estimated If mRNA were extracted from 10 cells (which would correspond to about 0 5 μg of poly(A) RNA), and if pnmers were present in about 10-100 fold concentration excess—as is called for in a typical protocol, e g Sambrook et al, Molecular Cloning, Second Edition, page 8 61 (10 μL 1 8 kb mRNA at 1 mg/mL equals about 1 68 x 10 " 1 1 moles and 10 μL 18-mer _9 pnmcr at 1 mg/mL equals about 1 68 x 10 moles), then the total number of tag- polynucleotide conjugates m a cDNA library would simply be equal to or less than the starting number of mRNAs, or about 5 x 10 vectors containing tag-polynucleotide conjugates (again this assumes that each step m cDNA construction — first strand synthesis, second strand synthesis, and hgation into a vector ~ occurs with perfect efficiency), which is a very conservative estimate The actual number is significantly less If a sample of n tag-polynucleotide conjugates are randomly drawn from a reaction mixture—as could be effected by taking a sample volume, the probability of drawing conjugates having the same tag is described by the Poisson distribution, P(r)=e (λ) /r, here r is the number of conjugates having the same tag and λ=np, where p is the probability of a given tag being selected If n=10 6 and p=l/(l 34 x 10 8 ), then λ= 00746 and P(2)=2 76 x 10 Thus, a sample of one million molecules gives rise to an expected number of doubles well withm the preferred range Such a sample is readily obtained as follows Assume that the 5 x 10 mRNAs are perfectly converted into 5 x 10 vectors with tag-cDN A conjugates as inserts and that the 5 x 10 vectors are in a reaction solution having a volume of 100 μl Four 10-fold senal dilutions may be carried out by transferring 10 μl from the original solution into a vessel containing 90 μl of an appropriate buffer, such as TE This process may be repeated for three additional dilutions to obtain a 100 μl solution containing 5 x 10 vector molecules per μl A 2 μl aliquot from this solution yields 10 vectors containing tag-cDNA conjugates as inserts This sample is then amplified by straight forward transformation of a competent host cell followed by cultuπng Of course, as mentioned above, no step in the above process proceeds with perfect efficiency In particular, when vectors are employed to amplify a sample of tag- polynucleotide conjugates, the step of transforming a host is very inefficient Usually, no more than 1% of the vectors are taken up by the host and replicated Thus, for such a method of amplification, even fewer dilutions would be required to obtain a sample of 10 conjugates A repertoire of oligonucleotide tags can be conjugated to a population of polynucleotides in a number of ways, including direct enzymatic hgation, amplification, e g via PCR, using primers containing the tag sequences, and the like The initial hgating step produces a very large population of tag-polynucleotide conjugates such that a single tag is generally attached to many different polynucleotides However, as noted above, by taking a sufficiently small sample of the conjugates, the probability of obtaining "doubles," I e the same tag on two different polynucleotides, can be made negligible Generally, the larger the sample the greater the probability of obtaining a double Thus, a design trade-off exists between select g a large sample of tag-polynucleotide conjugates— which, for example, ensures adequate coverage of a target polynucleotide in a shotgun sequencing operation or adequate representation of a rapidly changing mRNA pool, and selecting a small sample which ensures that a minimal number of doubles will be present In most embodiments, the presence of doubles merely adds an additional source of noise or, in the case of sequencing, a minor complication in scanning and signal processing, as microparticles giving multiple fluorescent signals can simply be ignored As used herein, the term "substantially all" in reference to attaching tags to molecules, especially polynucleotides, is meant to reflect the statistical nature of the sampling procedure employed to obtain a population of tag-molecule conjugates essentially free of doubles The meaning of substantially all in terms of actual percentages of tag-molecule conjugates depends on how the tags are being employed Preferably, for nucleic acid sequencing, substantially all means that at least eighty percent of the polynucleotides have unique tags attached More preferably, it means that at least ninety percent of the polynucleotides have unique tags attached Still more preferably, it means that at least ninety- five percent of the polynucleotides have unique tags attached And, most preferably, it means that at least ninety-nine percent of the polynucleotides have unique tags attached Preferably, when the population of polynucleotides consists of messenger RNA (mRNA), oligonucleotides tags may be attached by reverse transcribing the mRNA with a set of primers preferably containing complements of tag sequences An exemplary set of such primers could have the following sequence 5 ' -mRNA- [A] n -3 ' [T] 19 GG[W,W, ,C] QACCAGCTGATC-5 ' -biotin where "[W,W,W,C]c;" represents the sequence of an oligonucleotide tag of mne subumts of four nucleotides each and "fW,W,W,C]" represents the subunit sequences listed above, l e "W" represents T or A The underlined sequences identify an optional restriction endonuclease site that can be used to release the polynucleotide from attachment to a solid phase support via the biot , if one is employed For the above primer, the complement attached to a microparticle could have the form 5 ' - [G, , , W] gTGG-linker-raicroparticle After reverse transcnption, the mRNA is removed, e g by RNase H digestion, and the second strand of the cDNA is synthesized using, for example, a pnmer of the following form (SEQ ID NO 3) 5 ' -NRRGATCYNNN-3 ' where N is any one of A, T, G, or C, R is a punne-containing nucleotide, and Y is a pyπmidine-contaimng nucleotide This particular primer creates a Bst Y 1 restriction site in the resulting double stranded DNA which, together with the Sal I site, facilitates clomng to a vector with, for example, Bam HI and Xho I sites After Bst Yl and Sal I digestion, the exemplary conjugate would have the form 5 ' -RCGACCA [ C , , , ] 9 GG [T ] 1 9 - cDNA -NNNR GGT [ G, W , , W ] 9 CC [A] 1 9 - rDNA -NNNYCTAG-5 ' The polynucleotide-tag conjugates may then be manipulated using standard molecular biology techniques For example, the above conjugate— which is actually a mixture-may be inserted mto commercially available clomng vectors, e g Stratagene Cloning System (La Jolla, CA), transfected into a host, such as a commercially available host bacteria, which is then cultured to increase the number of conjugates The cloning vectors may then be isolated using standard techniques, e g Sambrook et al, Molecular Cloning, Second Edition (Cold Spring Harbor Laboratory, New York, 1989) Alternatively, appropnate adaptors and pnmers may be employed so that the conjugate population can be increased by PCR Preferably, when the hgase-based method of sequencing is employed, the Bst Yl and Sal I digested fragments are cloned into a Bam HI-/Xho I-digested vector having the following smgle-copy restriction sites 5'-GAGGATGCCTTTATGGATCCACTCGAGATCCCAATCCA-3' Fokl Ba HI Xhol This adds the Fok I site which will allow initiation of the sequencing process discussed more fully below Tags can be conjugated to cDNAs of existing hbranes by standard cloning methods cDNAs are excised from their existing vector, isolated, and then ligated into a vector contaimng a repertoire of tags Preferably, the tag-containing vector is Imeanzed by cleavmg with two restriction enzymes so that the excised cDNAs can be ligated m a predetermined orientation The concentration of the Imeanzed tag-containing vector is m substantial excess over that of the cDNA inserts so that hgation provides an inherent sampling of tags A general method for exposing the single stranded tag after amplification involves digesting a target polynucleotide-contaimng conjugate with the 5'— >3' exonuclease activity of T4 DNA polymerase, or a like enzyme When used m the presence of a single deoxynucleoside tnphosphate, such a polymerase will cleave nucleotides from 3' recessed ends present on the non-template strand of a double stranded fragment until a complement of the single deoxynucleoside tnphosphate is reached on the template strand When such a nucleotide is reached the 5'->3' digestion effectively ceases, as the polymerase's extension activity adds nucleotides at a higher rate than the excision activity removes nucleotides Consequently, single stranded tags constructed with three nucleotides are readily prepared for loading onto solid phase supports The technique may also be used to preferentially methylate interior Fok I sites of a target polynucleotide while leaving a single Fok I site at the terminus of the polynucleotide unmethylated First, the terminal Fok I site is rendered single stranded using a polymerase with deoxycytidine tnphosphate The double stranded portion of the fragment is then methylated, after which the single stranded terminus is filled in with a DNA polymerase the presence of all four nucleoside tπphosphates, thereby regenerating the Fok I site Clearly, this procedure can be generalized to endonucleases other than Fok I After the oligonucleotide tags are prepared for specific hybridization, e g by rendering them single stranded as descπbed above, the polynucleotides are mixed with microparticles containing the complementary sequences of the tags under conditions that favor the formation of perfectly matched duplexes between the tags and their complements There is extensive guidance in the literature for creating these conditions Exemplary references providing such guidance include Wetmur, Cntical Reviews in Biochemistry and Molecular Biology, 26 227-259 (1991), Sambrook et al, Molecular Cloning A Laboratory Manual, 2nd Edition (Cold Spnng Harbor Laboratory, New York, 1989), and the like Preferably, the hybndization conditions are sufficiently stringent so that only perfectly matched sequences form stable duplexes Under such conditions the polynucleotides specifically hybridized through their tags may be ligated to the complementary sequences attached to the microparticles Finally, the microparticles are washed to remove polynucleotides with un gated and/or mismatched tags When CPG microparticles conventionally employed as synthesis supports are used, the density of tag complements on the microparticle surface is typically greater than that necessary for some sequencing operations That is, in sequencing approaches that require successive treatment of the attached polynucleotides with a variety of enzymes, densely spaced polynucleotides may tend to inhibit access of the relatively bulky enzymes to the polynucleotides In such cases, the polynucleotides are preferably mixed with the microparticles so that tag complements are present in significant excess, e g from 10 1 to 100 1, or greater, over the polynucleotides This ensures that the density of polynucleotides on the microparticle surface will not be so high as to inhibit enzyme access Preferably, the average lnter-polynucleotide spacing on the microparticle surface is on the order of 30- 100 nm Guidance in selecting ratios for standard CPG supports and Ballotmi beads (a type of solid glass support) is found in Maskos and Southern, Nucleic Acids Research, 20 1679- 1684 (1992) Preferably, for sequencing applications, standard CPG beads of diameter in the range of 20-50 μm are loaded with about 10^ polynucleotides, and glycidalmethacrylate (GMA) beads available from Bangs Laboratories (Carmel, IN) of diameter in the range of 5- 10 μm arc loaded with a few tens of thousand polynucleotide, e g 4 x 10"^ to 6 x 10^ In the preferred embodiment, tag complements for sorting are synthesized on microparticles combinatonally, thus, at the end of the synthesis, one obtains a complex mixture of microparticles from which a sample is taken for loading tagged polynucleotides The size of the sample of microparticles will depend on several factors, including the size of the repertoire of tag complements, the nature of the apparatus for used for observing loaded mιcropartιcles~e g its capacity, the tolerance for multiple copies of microparticles with the same tag complement (l e "bead doubles"), and the like The following table provide guidance regarding microparticle sample size, microparticle diameter, and the approximate physical dimensions of a packed array of microparticles of various diameters Microparticle 5 μm 10 μm 20 μm 40 μm diameter Max no polynucleotides loaded at 1 per 3 x 10 5 1 26 x 10 6 5 x 10 6 10 5 sq angstrom Approx area of monolayer of 10 6 microparticles 45 x 45 cm 1 x 1 cm 2 x 2 cm 4 x 4 cm The probability that the sample of microparticles contains a given tag complement or is present in multiple copies is described by the Poisson distribution, as indicated in the following table Table VI High Specificity Sorting and Panning The kinetics of sorting depends on the rate of hybridization of oligonucleotide tags to their tag complements which, in turn, depends on the complexity of the tags in the hybridization reaction Thus, a trade off exists between sorting rate and tag complexity, such that an increase in sorting rate may be achieved at the cost of reducing the complexity of the tags involved in the hybridization reaction As explained below, the effects of this trade off may be ameliorated by "panning " Specificity of the hybridizations may be increased by taking a sufficiently small sample so that both a high percentage of tags in the sample are unique and the nearest neighbors of substantially all the tags in a sample differ by at least two words This latter condition may be met by taking a sample that contains a number of tag-polynucleotide conjugates that is about 0 1 percent or less of the size of the repertoire being employed For example, if tags are constructed with eight words selected from Table II, a repertoire of 8^, or about 1 67 x 10 , tags and tag complements are produced In a library of tag-cDNA conjugates as described above, a 0 1 percent sample means that about 16,700 different tags are present If this were loaded directly onto a repertoire-equivalent of microparticles, or this example a sample of 1 67 x 10 microparticles, then only a sparse subset of the sampled microparticles would be loaded The density of loaded microparticles can be increase— for example, for more efficient sequencing— by undertaking a "panning" step which the sampled tag-cDNA conjugates are used to separate loaded microparticles from unloaded microparticles Thus, in the example above, even though a "0 1 percent" sample contams only 16,700 cDNAs, the sampling and panning steps may be repeated until as many loaded microparticles as desired are accumulated Alternatively, loaded microparticles may be separated from unloaded microparticles by a fluorescently activated cell sorting (FACS) instrument using conventional protocols, e g tag-cDNA conjugates may be fluorescently label m the technique described below by providing fluorescently labelled nght primer After loading and FACS sorting, the label may be cleaved prior to hgating encoded adaptors, e g by Dpn I or like enzyme that recognize methylated sites A panning step may be implemented by providing a sample of tag-cDNA conjugates each of which contams a capture moiety at an end opposite, or distal to, the oligonucleotide tag Preferably, the capture moiety is of a type which can be released from the tag-cDNA conjugates, so that the tag-cDNA conjugates can be sequenced with a single-base sequencmg method Such moieties may compnse biotin, digoxigemn, or like ligands, a tnplex binding region, or the like Preferably, such a capture moiety comprises a biotin component Biotin may be attached to tag-cDNA conjugates by a number of standard techniques If appropriate adapters contaimng PCR primer binding sites arc attached to tag-cDNA conjugates, biotm may be attached by using a biotinylated primer in an amplification after sampling Alternatively, if the tag-cDNA conjugates are inserts of clomng vectors, biotin may be attached after excising the tag-cDNA conjugates by digestion with an appropriate restriction enzyme followed by isolation and filling m a protruding strand distal to the tags with a DNA polymerase in the presence of biotinylated undine tnphosphate After a tag-cDNA conjugate is captured, it may be released from the biotin moiety in a number of ways, such as by a chemical linkage that is cleaved by reduction, e g Herman et al, Anal Biochem , 156 48-55 (1986), or that is cleaved photochemically, e g Olejnik et al, Nucleic Acids Research, 24 361-366 (1996), or that is cleaved enzymatically by introducing a restriction site in the PCR primer The latter embodiment can be exemplified by considering the library of tag-polynucleotide conjugates described above 5'-RCGACCA[C,W, ,W] 9 GG[T] 19 - cDNA -NNNR GGT[G,W,W,W] 9 CC[A] 19 - rDNA -NNNYCTAG-5' The following adapters may be ligated to the ends of these fragments to permit amplification by PCR 5'- xxxxxxxxxxxxxxxxxxxx XXXXXXXXXXXXXXXXXXXXYGAT Right Adapter GATCZZACTAGTZZZZZZZZZZZZ-3' ZZTGATCAZZZZZZZZZZZZ Left Adapter ZZTGATCAZZZZZZZZZZZZ-5 ' -biotm Left Primer where "ACTAGT" is a Spe I recogmtion site (which leaves a staggered cleavage ready for single base sequencing), and the X's and Z's are nucleotides selected so that the annealing and dissociation temperatures of the respective primers are approximately the same After hgation of the adapters and amplification by PCR using the biotinylated primer, the tags of the conjugates are rendered single stranded by the exonuclease activity of T4 DNA polymerase and conjugates are combined with a sample of microparticles, e g a repertoire equivalent, with tag complements attached After annealing under stringent conditions (to minimize mis-attachment of tags), the conjugates are preferably ligated to their tag complements and the loaded microparticles are separated from the unloaded microparticles by capture with avidinated magnetic beads, or like capture technique Returning to the example, this process results in the accumulation of about 10,500 (=16,700 x 63) loaded microparticles with different tags, which may be released from the magnetic beads by cleavage with Spe I By rcpcatmg this process 40-50 tunes with new samples of microparticles and tag-cDNA conjugates, 4-5 x 10 3 cDNAs can be accumulated by poolmg the released microparticles The pooled microparticles may then be simultaneously sequenced by a single-base sequencing technique Determining how many times to repeat the sampling and panning steps— or more generally, determining how many cDNAs to analyze, depends on one's objective If the objective is to monitor the changes m abundance of relatively common sequences, e g making up 5% or more of a population, then relatively small samples, I e a small fraction of the total population size, may allow statistically significant estimates of relative abundances On the other hand, if one seeks to monitor the abundances of rare sequences, e g making up 0 1% or less of a population, then large samples are required Generally, there is a direct relationship between sample size and the reliability of the estimates of relative abundances based on the sample There is extensive guidance m the literature on determining appropriate sample sizes for making reliable statistical estimates, e g Koller et al, Nucleic Acids Research, 23 185- 191 (1994), Good, Biometnka, 40 16-264 (1953), Bunge et al, J Am Stat Assoc , 88 364- 373 (1993), and the like Preferably, for monitoring changes in gene expression based on the analysis of a senes of cDNA branes containing 10^ to 10^ independent clones of 3 0-3 5 x 10 4 different sequences, a sample of at least 10 4 sequences are accumulated for analysis of each library More preferably, a sample of at least 10^ sequences are accumulated for the analysis of each library, and most preferably, a sample of at least 5 x 10^ sequences are accumulated for the analysis of each library Alternatively, the number of sequences sampled is preferably sufficient to estimate the relative abundance of a sequence present at a frequency within the range of 0 1% to 5% with a 95% confidence limit no larger than 0 1% of the population size Construction of a Tag Library An exemplary tag library is constructed as follows to form the chemically synthesized 9-word tags of nucleotides A, G, and T defined by the formula 3'-TGGC-[ 4 (A,G,T)9]-CCCCp where "[ 4 ((A,G,T)9]" indicates a tag mixture where each tag consists of nine 4-mer words of A, G, and T, and "p" indicate a 5' phosphate This mixture is ligated to the following nght and left pnmer binding regions (SEQ ID NO 4 & 5) 5 ' - AGTGGCTGGGCATCGGACCG 5 ' - GGGGCCCAGTCAGCGTCGAT TCACCGACCCGTAGCCp GGGTCAGTCGCAGCTA LEFT RIGHT The right and left pnmcr bmdmg regions are ligated to the above tag mixture, after which the smgle stranded portion of the ligated structure is filled with DNA polymerase then mixed with the right and left primers indicated below and amplified to give a tag library Left Primer 5 '- AGTGGCTGGGCATCGGACCG 5'- AGTGGCTGGGCATCGGACCG- [ 4 < (A,G, ) 9] -GGGGCCCAGTCAGCGTCGAT TCACCGACCCGTAGCC GGC- [ < (A,G,T) 9] -CCCCGGGTCAGTCGCAGCTA CCCCGGGTCAGTCGCAGCTA-5' Right Primer The underlined portion of the left primer binding region indicates a Rsr II recogmtion site The left-most underlined region of the nght pnmer binding region indicates recognition sites for Bsp 1201, Apa I, and Eco O 1091, and a cleavage site for Hga I The right-most underlined region of the right primer binding region indicates the recognition site for Hga I Optionally, the nght or left primers may be synthesized with a biotin attached (using conventional reagents, e g available from Clontech Laboratories, Palo Alto, CA) to facilitate purification after amplification and/or cleavage Construction of a Plasmid Library of Tag-Polynucleotide Coniugates for cDNA "Signature" Sequencing Using Encoded Adaptors cDNA is produced from an mRNA sample by conventional protocols using pGGCCCTi5(A or G or C) as a pnmer for first strand synthesis anchored at the boundary of the poly A region of the mRNAs and Ns(A or T)GATC as the primer for second strand synthesis That is, both are degenerate pnmers such that the second strand primer is present in two forms and the first strand pnmer is present in three forms The GATC sequence in the second strand pnmer corresponds to the recognition site of Mbo I, other four base recognition sites could be used as well, such as those for Bam HI, Sph I, Eco RI, or the like The presence of the A and T adjacent to the restriction site of the second strand pnmer ensures that a stripping and exchange reaction can be used in the next step to generate a five-base 5' overhang of "GGCCC" The first strand primer is annealed to the mRNA sample and extended with reverse transcnptase, after which the RNA strand is degraded by the RNase H activity of the reverse transcnptase leaving a single stranded cDNA The second strand pnmer is annealed and extended with a DNA polymerase using conventional protocols After second strand synthesis, the resulting cDNAs are methylated with CpG methylase (New England Biolabs, Beverly, MA) using manufacturer's protocols The 3' strands of the cDNAs are then cut back with the above-mentioned stripping and exchange reaction using T4 DNA polymerase in the presence of dATP and dTTP, after which the cDNAs are ligated to the tag library described above previously cleaved with Hga I to give the following construct 5'-biotin- | primer binding site TAG Apa I cDNA Rsr II site Mbo I site Separately, the following cloning vector is constructed, e.g. starting from a commercially available plasmid, such as a Bluescript phagemid (Stratagene, La Jolla, CA)(SEQ ID NO 6) primer bmdmg site Ppu MI site I (pl -CAAATTTG-CCTAGG-AGAAGGAGAAGGAGAAGG- t T Pme I site The plasmid is cleaved with Ppu MI and Pme I (to give a Rsr II-compatιble end and a flush end so that the insert is oriented) and then methylated with DAM methylase The tag- containing construct is cleaved with Rsr II and then ligated to the open plasmid, after which the conjugate is cleaved with Mbo I and Bam HI to permit hgation and closing of the plasmid The plasmids are then amplified and isolated for use in accordance with the invention Example 1 Sequencing a Target Polynucleotide Amplified from pGEM7Z Identification of Nucleotides bv Cycles of Ligation and Cleavage In this example, a segment of plasmid pGEM7Z (Promega, Madison, WI) is amplified and attached to glass beads via a double stranded DNA linker, one strand of which is synthesized directly onto (and therefore covalently linked to) the beads After the ends of the target polynucleotide are prepared for gation to the encoded adapters, m each cycle of hgation and cleavage, a mixture of encoded adaptors (1024 different adaptors in all) is applied to the target polynucleotides so that only those adaptors whose protrudmg strands form perfectly matched duplexes with the target polynucleotides are ligated Each of 16 fluorescently labelled tag complements are then applied to the polynucleotide-adaptor conjugates under conditions that permit hybridization of only the correct tag complements The presence or absense of fluorescent signal after washing indicates the presence or absence of a particular nucleotide at a particular location The sequencing protocol of this example is applicable to multiple target polynucleotides sorted onto one or more solid phase supports as described in Brenner, International patent applications PCT/US95/I2791 and PCT/US96/09513 (WO 96/12041 and WO 96/4101 1) A 47-mer oligonucleotide is synthesized directly on Ballotini beads ( 040- 075 mm, Jencons Scientific, Bndgeville, PA) using a standard automated DNA synthesizer protocol The complementary strand to the 47-mer is synthesized separately and purified by HPLC When hybridized the resulting duplex has a Bst XI restriction site at the end distal from the bead The complementary strand is hybndized to the attached 47-mer in the following mixture 25 μL complementary strand at 200 pmol/μL, 20 mg Ballotini beads with the 47- mer, 6 μL New England Biolabs #3 restnction buffer (from lOx stock solution), and 25 μL distilled water The mixture is heated to 93°C and then slowly cooled to 55°C, after which 40 units of Bst XI (at 10 units/μL) is added to bring the reaction volume to 60 μL The mixture is incubated at 55°C for 2 hours after which the beads are washed three times m TE (pH 8 0) The segment ofpGEM7Z to be attached to the beads is prepared as follows Two PCR primers were prepared using standard protocols (SEQ ID NO 7 and SEQ ID NO 8) Primer 1 : 5 ' -CTAAACCATTGGTATGGGCCAGTGAATTGTAATA Primer 2: 5 ' -CGCGCAGCCCGCATCGTTTATGCTACAGACTGTC- AGTGCAGCTCTCCGATCCAAA The PCR reaction mixture consists of the following 1 μl pGEM7Z at 1 ng/μl, 10 μl pnmer 1 at 10 pmol/μl, 10 μl primer 2 at 10 pmol/μl, 10 μl deoxyπbonucleotide tπphosphates at 2 5 mM, 10 μl lOx PCR buffer (Perkin-Elmer), 0 5 μl Taq DNA polymerase at 5 units/μl, and 58 μl distilled water to give a final volume of 100 μl The reaction mixture was subjected to 25 cycles of 93°C for 30 sec, 60°C for 15 sec, and 72°C for 60 sec, to give a 172 basepair product, which is successively digested w th Bbv I (100 μl PCR reaction mixture, 12 μl lOx # 1 New England Biolabs buffer, 8 μl Bbv I at 1 unit μl incubate at 37°C for 6 hours) and with Bst XI (to the Bbv I reaction mixture is added 5 μl 1 M NaCl, 67 μl distilled water, and 8 μl Bst XI at 10 units/μl, and the resulting mixture is incubated at 55°C for 2 hours) After passing the above reaction mixture through a Centπcon 30 (Amicon, Inc ) spm column following manufacturer's protocol, the Bbv I/Bst Xl-restπcted fragment is ligated to the double stranded linker attached to the Ballotini beads in the following mixture 17 μl Bbv I/Bst Xl-restπcted fragment (10 μg), 10 μl beads (20 mg), 6 ml lOx hgation buffer (New England Biolabs, referred to below as NEB), 5 μl T4 DNA hgase at 2000 units/μl, and 22 μl distilled water, which mixture is incubated at 25°C for 4 hours, after which the beads are washed 3 times with TE (pH 8 0), leaving the following target polynucleotide (SEQ ID NO 9) for sequencing havmg a 5' phosphate . . . AGCTACCCGATC [BEAD] — . . . TCGATGGGCTAGATTTp-5' The 5' phosphate is removed by treating the bead mixture with an alkaline phosphatase, e g from calf intestine, available from New England Biolabs (Beverly MA), using manufacturer's protocol The top strands of the following 16 sets of 64 encoded adaptors (SEQ ID NO 10 through SEQ ID NO 25) are each separately synthesized on an automated DNA synthesizer (model 392 Applied Biosystems, Foster City) using standard methods The bottom strand, which is the same for all adaptors, is synthesized separately then hybridized to the respective top strands SEQ ID Encoded Adaptor NO . 10 5 ' -pANNNTACAGCTGCATCCCttggcgctgagg pATGCACGCGTAGGG-5' 11 5'-pNANNTACAGCTGCATCCCtgggcctgtaag pATGCACGCGTAGGG-5' 12 5'-pCNNNTACAGCTGCATCCCttgacgggtctc pATGCACGCGTAGGG-5' 13 5'-pNCNNTACAGCTGCATCCCtgcccgcacagt pATGCACGCGTAGGG-5' 14 5 '-pGNNNTACAGCTGCATCCCttcgcctcggac pATGCACGCGTAGGG-5' 15 5 '-pNGNNTACAGCTGCATCCCtgatccgctagc pATGCACGCGTAGGG-5 ' 16 5 '-pTNNNTACAGCTGCATCCCttccgaacccgc pATGCACGCGTAGGG-5' 17 5'-pNTNNTACAGCTGCATCCCtgagggggatag pATGCACGCGTAGGG-5 ' 18 5 '-pNNANTACAGCTGCATCCCttcccgctacac pATGCACGCGTAGGG-5 ' 19 5 '-pNNNATACAGCTGCATCCCtgactccccgag pATGCACGCGTAGGG-5' 20 5 '-pNNCNTACAGCTGCATCCCtgtgttgcgcgg pATGCACGCGTAGGG-5 ' 21 5 '-pNNNCTACAGCTGCATCCCtctacagcagcg pATGCACGCGTAGGG-5 ' 22 5 ' -pNNGNTACAGCTGCATCCCtgtcgcgtcgtt pATGCACGCGTAGGG-5 ' 23 5 ' -pNNNGTACAGCTGCATCCCtcggagcaacct pATGCACGCGTAGGG-5' 24 5 '-pNNTNTACAGCTGCATCCCtggtgaccgtag pATGCACGCGTAGGG-5' 25 5 '-pNNNTTACAGCTGCATCCCtcccctgtcgga pATGCACGCGTAGGG-5 ' where N and p are as defined above, and the nucleotides indicated in lower case letters are the 12-mer oligonucleotide tags. Each tag differs from every other by 6 nucleotides. Equal molar quantities of each adaptor are combined in NEB buffer No. 2 (New England Biosciences, Beverly, MA) to form a mixture at a concentration of 1000 pmol/μl. Each of the 16 tag complements are separately synthesized as amino-derivatized oligonucleotides and are each labelled with a fluorescem molecule (e g FAM, an NHS-ester of fluorescein, available from Molecular Probes, Eugene, OR) which is attached to the 5' end of the tag complement through a polyethylene glycol linker (Clonetech Laboratories, Palo Alto, CA) The sequences of the tag complements are simply the 12-mer complements of the tags listed above Ligation of the adaptors to the target polynucleotide is carried out m a mixture consisting of 5 μl beads (20 mg), 3 μL NEB lOx hgase buffer, 5 μL adaptor mix (25 nM), 2 5 μL NEB T4 DNA hgase (2000 umts/μL), and 14 5 μL distilled water The mixture is mcubated at 16°C for 30 minutes, after which the beads arc washed 3 times in TE (pH 8 0) After centntugation and removal of TE, the 3' phosphates of the ligated adaptors arc removed by treating the polynucleotide-bead mixture with calf intestmal alkaline phosphatase (CIP) (New England Biolabs, Beverly, MA), usmg the manufacturer's protocol After removal of the 3' phosphates, the CIP may be inactivated by proteolytic digestion, e g usmg Pronase τ (available form Boermger Mannhiem, Indianapolis, IN), or an equivalent protease, with the manufacturer's protocol The polynucleotide-bead mixture is then washed and treated with a mixture of T4 polynucleotide k ase and T4 DNA hgase (New England Biolabs, Beverly, MA) to add a 5' phosphate at the gap between the target polynucleotide and the adaptor to complete the hgation of the adaptors to the target polynucleotide The bead- polynucleotide mixture is then washed in TE Separately, each of the labelled tag complements is applied to the polynucleotide-bead mixture under conditions which permit the formation of perfectly matched duplexes only between the oligonucleotide tags and their respective complements, after which the mixture is washed under stringent conditions, and the presence or absense of a fluorescent signal is measured Tag complements are applied in a solution consisting of 25 nM tag complement 50 mM NaCl, 3 mM Mg, 10 mM Tns-HCl (pH 8 5), at 20°C, incubated for 10 minutes, then washed in the same solution (without tag complement) for 10 minute at 55°C After the four nucleotides are identified as described above, the encoded adaptors are cleaved from the polynucleotides with Bbv I usmg the manufacturer's protocol After an initial hgation and identification, the cycle of hgation, identification, and cleavage is repeated three times to give the sequence of the 16 terminal nucleotides of the target polynucleotide Figure 4 illustrates the relative fluorescence from each of four tag complements applied to identify nucleotides at positions 5 through 16 (from the most distal from the bead to the most proximal to the bead) Example 2 Construction and Sorting of cDNA Library for Signature Sequencing with Encoded Adaptors In this example, a cDNA library is constructed in which an oligonucleotide tag consisting of 8 four-nucleotide "words" is attached to each cDNA As described above, the repertoire of oligonucleotide tags of this size is sufficiently large (about 10 8 ) so that if the cDNAs are synthesized from a population of about 10 6 mRNAs, then there is a high probability that each cDNA will have a unique tag for sorting After mRNA extraction, first strand synthesis is carried out in the presence of 5-Mc-dCTP (to block certain cDNA restriction sites) and a biotinylated pnmer mixture containing the oligonucleotide tags After conventional second strand synthesis, the tag-cDNA conjugates are cleaved with Dpn II (which is unaffected by the 5-Me-deoxycytosιnes), the biotinylated portions are separated from the reaction mixture using streptavidm-coated magnetic beads, and the tag-cDNA conjugates are recovered by cleavmg them from the magnetic beads via a Bsm BI site carried by the biotinylated pnmer The Bsm BI-Dpn II fragment containing the tag-cDNA conjugate is then inserted mto a plasmid and amplified After isolation of the plasmids, tag-cDNA conjugates are amplified out of the plasmids by PCR in the presence of 5-Me-dCTP, usmg biotinylated and fluorescently labelled primers containing pre-defined restnction endonuclease sites After affinity puπfication with streptavidin coated magnetic beads, the tag-cDNA conjugates are cleaved from the beads, treated with T4 DNA polymerase in the presence of dGTP to render the tags single stranded, and then combined with a repertoire of GMA beads having tag complements attached After stringent hybridization and hgation, the GMA beads are sorted via FACS to produce an enriched population of GMA beads loaded with cDNAs The enriched population of loaded GMA beads are immobilized in a planar array in a flow chamber where base-by-base sequence takes place using encoded adaptors Approximately 5 μg of poly(A + ) mRNA is extracted from DBY746 yeast cells using conventional protocols First and second strand cDNA synthesis is carried out by combining 100-150 pmoles of the following primer (SEQ ID NO 26) 5 ' -biotin-ACTAATCGTCTCACTATTTAATTAA [ W , W , W , G ] 8 CC ( T ) ι gV- 3 ' with the poly(A+) mRNA using a Stratagene (La Jolla, CA) cDNA Synthesis Kit in accordance with the manufacturer's protocol This results in cDNAs whose first stand deoxycytosmes are methylated at the 5-carbon position In the above formula, "V" is G, C, or A, "IW,W,W,G]" is a four-nucleotide word selected from Table II as described above, the single underlined portion is a Bsm BI recognition site, and the double underlined portion is a Pac I recognition site After size fractionation (GIBCO-BRL cDNA Size Fractionation Kit) using conventional protocols, the cDNAs are digested with Dpn II (New England Bioscience, Beverly, MA) using manufacturer's protocol and affinity purified with streptavidin-coated magnetic beads (M-280 beads, Dynal A S , Oslo, Norway) The DNA captured by the beads is digested with Bsm BI to release the tag-cDNA conjugates for cloning into a modified pBCSK" vector (Stratagene, La Jolla, CA) usmg standard protocols The pBCSK" vector is modified by adding a Bbs I site by inserting the following fragment (SEQ ID NO 27) into the Kpn I/Eco RV digested vector CGAAGACCC 3 ' -CATGGCTTCTGGGGATA-5 ' Bsm BI/Dpn II digested tag-cDNA conjugate is inserted in the pBCSK" which is previously digested with Bbs I and Bam HI After hgation, the vector is transfected into the manufacturer's recommended host for amplification After isolating the above pBCSK " vector from a standard plasmid mimprep, the tag- cDNA conjugates are amplified by PCR in the presence of 5-Me-dCTP using 20-mer primers complementary to vector sequences flanking the tag-cDNA insert The "upstream" pnmer, l e adjacent to the tag, is biotinylated and the "downstream" primer, I e adjacent to the cDNA, is labelled with fluorescein After amplification, the PCR product is affinity punfied then cleaved with Pac I to release fluorescently labelled tag-cDNA conjugates The tags of the conjugates are rendered smgle stranded by treating them with T4 DNA polymerase in the presence of dGTP After the reaction is quenched, the tag-cDNA conjugate is punfied by phenol-chloroform extraction and combined with 5 5 mm GMA beads carrying tag complements, each tag complement having a 5' phosphate Hybridization is conducted under stringent conditions in the presence of a thermal stable hgase so that only tags forming perfectly matched duplexes with their complements arc ligated The GMA beads are washed and the loaded beads are concentrated by FACS sorting, using the fluorescently labelled cDNAs to identify loaded GMA beads The tag-cDNA conjugates attached to the GMA beads are digested with Dpn II to remove the fluorescent label and treated with alkaline phosphatase to prepare the cDNAs for sequencing The following cleavage adaptor (SEQ ID NO 28) is ligated to the Dpn II-dιgested and phosphatase treated cDNAs 5 '-pGATCAGCTGCTGCAAATTT pTCGACGACGTTTAAA after which the 3' phosphate is removed by alkaline phosphatase, the 5' strand of the cDNA is treated with T4 DNA kinase, and the nick between the cleavage adaptor and cDNA is ligated After cleavage by Bbv I, the encoded adaptors of Example 1 are ligated to the ends of the cDNAs as descnbed above A flow chamber (500) diagrammatically represented in Figure 5 is prepared by etching a cavity having a fluid inlet (502) and outlet (504) in a glass plate (506) usmg standard micromachimng techniques, e g Ekstrom et al, International patent application PCT/SE91/00327 (WO 91/16966), Brown, U S patent 4,911,782, Harπson et al, Anal Chem 64 1926-1932 (1992), and the like The dimension of flow chamber (500) are such that loaded microparticles (508), e g GMA beads, may be disposed in cavity (510) in a closely packed planar monolayer of 100-200 thousand beads Cavity (510) is made into a closed chamber with inlet and outlet by anodic bonding of a glass cover slip (512) onto the etched glass plate (506), e g Pomerantz, U S patent 3,397,279 Reagents are metered into the flow chamber from syringe pumps (514 through 520) through valve block (522) controlled by a microprocessor as is commonly used on automated DNA and peptide synthesizers, e g Bπdgham et al, U S patent 4,668,479, Hood et al, U S patent 4,252,769, Barstow et al, U S patent 5,203,368, Hunkapiller, U S patent 4,703,913, or the like Three cycles of hgation, identification, and cleavage are earned out in flow chamber (500) to give the sequences of 12 nucleotides at the termini of each of appoximately 100,000 cDNAs Nucleotides of the cDNAs are identified by hybridizing tag complements to the encoded adaptors as described in Example 1 Specifically hybndized tag complements are detected by exciting their fluorescent labels with illumination beam (524) from light source (526), which may be a laser, mercury arc lamp, or the like Illumination beam (524) passes through filter (528) and excites the fluorescent labels on tag complements specifically hybridized to encoded adaptors in flow chamber (500) Resulting fluorescence (530) is collected by confocal microscope (532), passed through filter (534), and directed to CCD camera (536), which creates an electronic image of the bead array for processing and analysis by workstation (538) Preferably, after each hgation and cleavage step, the cDNAs are treated with Pronase™ or like enzyme Encoded adaptors and T4 DNA hgase (Promega, Madison, WI) at about 0 75 units per μL are passed through the flow chamber at a flow rate of about 1-2 μL per minute for about 20-30 minutes at 16°C, after which 3' phosphates are removed from the adaptors and the cDNAs prepared for second strand hgation by passing a mixture of alkaline phosphatase (New England Bioscience, Beverly, MA) at 0 02 units per μL and T4 DNA kinase (New England Bioscience, Beverly, MA) at 7 units per μL through the flow chamber at 37°C with a flow rate of 1-2 μL per mmute for 15-20 minutes Ligation is accomplished by T4 DNA hgase ( 75 units per mL, Promega) through the flow chamber for 20-30 minutes Tag complements at 25 nM concentration arc passed through the flow chamber at a flow rate of 1-2 μL per minute for 10 minutes at 20°C, after which fluorescent labels carried by the tag complements are illuminated and fluorescence is collected The tag complements are melted from the encoded adaptors by passing hybridization buffer through the flow chamber at a flow rate of 1-2 μL per minute at 55°C for 10 minutes Encoded adaptors are cleaved from the cDNAs by passing Bbv I (New England Biosciences, Beverly, MA) at 1 unit/μL at a flow rate of 1-2 μL per minute for 20 minutes at 37°C APPENDIX I Exemplary computer program for generating minimally cross hybndizmg sets (single stranded tag/single stranded tag complement) Program tagN c c c Program tagN generates minimally cross-hybridizing c sets of subumts given I) N—subunit length, and ii) c an initial subunit sequence. tagN assumes that only c 3 of the four natural nucleotides are used in the tags. c c character*l subl(20) mteger*2 set (10000, 20) nbase(20) write {*,*) 'ENTER SUBUNIT LENGTH' read(*, 100)nsub 100 format (ι2) c c write {*,*) 'ENTER SUBUNIT SEQUENCE' read(*, 110) (subl(k) , =l,nsub) 110 format (20al) c c ndιff=10 c c c Let a=l c=2 g=3 & t=4 c c do 800 kk=l,nsub if (subl (kk) .eq. 'a' ) then mset (l,kk)=l endif if (subl (kk) .eq. 'c' ) then mset (l,kk)=2 endif if (subl (kk) .eq. 'g' ) then mset (l,kk)=3 endif if (subl (kk) .eq. 't ' ) then mset (1, kk)=4 endif 800 continue c c c Generate set of subumts differing from c subl by at least ndiff nucleotides. c c :D=I do 1000 kl=l,3 do 1000 k2=l,3 do 1000 k3=l,3 do 1000 k4=l,3 do 1000 k5=l,3 do 1000 k6=l,3 do 1000 k7=l,3 do 1000 k8=l,3 do 1000 k9=l,3 do 1000 kl0=l,3 do 1000 kll=l,3 do 1000 kl2=l,3 do 1000 kl3=l,3 do 1000 kl4=l,3 do 1000 kl5=l,3 do 1000 kl6=l,3 do 1000 kl7=l,3 do 1000 kl8=l,3 do 1000 kl9=l,3 do 1000 k20=l,3 c c nbase (1) kl nbase (2) =k2 nbase (3) =k3 nbase (4) =k4 nbase (5) k5 nbase (6) =k6 nbase (7) =k7 nbase (8) =k8 nbase (9) =k9 nbase (10) =kl0 nbase (11) =kll nbase (12) =kl2 nbase (13) =kl3 nbase (14) =kl4 nbase (15) =kl5 nbase (16) =kl6 nbase (17) =kl7 nbase (18) =kl8 nbase (19) =kl9 nbase (20) =k20 c c do 1250 nn=l,jj n=0 do 1200 j=l,nsub if (mset (nn, j ) . eq . and. nbase (j ) ne ,1 or. 1 mset (nn, j ) . eq . and. nbase ( j ) ne ,2 or. 2 mset (nn, j ) . eq .and. nbase (j ) ne 3 or. 3 mset (nn, j ) . eq .and. nbase (j ) ne 4) then n=n+l endif 1200 continue c c if (n.lt.ndiff) then goto 1000 endif 1250 continue c c 31=13+1 wnte(*,130) (nbase(ι) ,ι=l,nsub) ,33 do 1100 ι=l,nsub mset ( 3 ,1) =nbase ( ) 1100 continue c c 1000 continue c c write(*,*) 130 format (lOx,20 (lx, il) ,5x,ι5) write (*, *) write (*, 120) JJ 120 format (lx, 'Number of words=',ι5) end * + ++ + -* + ★★ + + * + + + *★ + * + +*** + ★ + * + ** + * + + * + -* ■■ * ■ -■•_. „■ -■ ★ ★★ + *** + * + + + * + + + * + + + * + +**** + + +* + + + + + + ,lr** --._. -A.+ APPENDIX II Exemplary computer program for generating minimally cross hybridizing sets (double stranded tag/single stranded tag complement) Program 3tagN c c c Program 3tagN generates minimally cross-hybridizmg c sets of triplex words given 1) N--subunιt length, (11) c an initial subunit sequence, and 111) the identity c of the nucleotides making up the subumts, i.e. c whether the subumts consist of all four c nucleotides, c or some subset of nucleotides. c c character*l subl (20) mteger*2 mset ( 10000, 20 ) , nbase (20 ) c c nsub=20 ndιff=6 c c write (*,*) 'ENTER SUBUNIT SEQUENCE: a & g only' read(*,110) (subl (k) , k=l,nsub) 110 format (20al) c c c Generate set of words differing from c subl by at least three ndiff nucleotides. c c c Translate a's & g's into numbers with a=l & g=2 c c then do 1000 kl=l,2 do 1000 k2=l,2 do 1000 k3=l,2 do 1250 nn=l,jj n=0 do 1200 j=l,nsub if(mset (nn, j ) . mset (nn, j ) . n=n+l endif 1200 continue c c if (n.lt.ndiff) then goto 1000 endif 1250 continue c __ -]=_] D+l write (*, 130) do 1100 ι=l, nsub mset(]], ι)=nbase (l) 1100 continue c c 1000 continue c c write {*, *) 130 format (5x,20 (lx,il) , 5x,ι5) write (*, *) wrιte(*,120) JJ 120 format (lx, 'Number of words=',ι5) c c end SEQUENCE LISTING (I) GENERAL INFORMATION: (i) APPLICANT: Lynx Therapeutics, Inc. (II) TITLE OF INVENTION: Massively Parallel Signature Sequencing by Ligation of Encoded Adaptors (ill) NUMBER OF SEQUENCES: 28 (iv) CORRESPONDENCE ADDRESS: (A) ADDRESSEE: Dehlmger & Associates (B) STREET: 350 Cambridge Avenue, Suite 250 (C) CITY: Palo Alto (D) STATE: CA (E) COUNTRY: USA (F) ZIP: 94306 (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 : (vii) PRIOR APPLICATION DATA: (A) APPLICATION NUMBER: US 08/689,587 (B) FILING DATE: 12-AUG-96 (vii) PRIOR APPLICATION DATA: (A) APPLICATION NUMBER: US 08/659,453 (B) FILING DATE: 06-JUN-96 (vm) ATTORNEY/AGENT INFORMATION: (A) NAME: Powers, Vincent M. (B) REGISTRATION NUMBER: 36,246 (C) REFERENCE/DOCKET NUMBER: 5525-0029.41/808-lwo (ix) TELECOMMUNICATION INFORMATION: (A) TELEPHONE: (415) 324-0880 (B) TELEFAX: (415) 324-0960 (i) SEQUENCE CHARACTERISTICS: (A) LENGTH: 28 nucleotides (B) TYPE: nucleic acid (C) STRANDEDNESS: double (D) TOPOLOGY: linear (xi) SEQUENCE DESCRIPTION: SEQ ID NO: 1: TGGATTCTAG AGAGAGAGAG AGAGAGAG 28 (2) INFORMATION FOR SEQ ID NO: 2: (l) SEQUENCE CHARACTERISTICS: (A) LENGTH: 16 nucleotides (B) TYPE: nucleic acid (C) STRANDEDNESS: double (D) TOPOLOGY: linear ( i) SEQUENCE DESCRIPTION: SEQ ID NO: 2: NNGGATGNNN NNNNNN 16 (2) INFORMATION FOR SEQ ID NO: 3: (l) SEQUENCE CHARACTERISTICS: (A) LENGTH: 11 nucleotides (B) TYPE: nucleic acid (C) STRANDEDNESS: single (D) TOPOLOGY: linear (Xl) SEQUENCE DESCRIPTION: SEQ ID NO: 3: NRRGATCYNN N 11 (2) INFORMATION FOR SEQ ID NO: 4: (1) SEQUENCE CHARACTERISTICS: (A) LENGTH: 20 nucleotides (B) TYPE: nucleic acid (C) STRANDEDNESS: double (D) TOPOLOGY: linear (xi) SEQUENCE DESCRIPTION: SEQ ID NO: : AGTGGCTGGG CATCGGACCG 20 (2) INFORMATION FOR SEQ ID NO: 5: (l) SEQUENCE CHARACTERISTICS: (A) LENGTH: 20 nucleotides (B) TYPE: nucleic acid (C) STRANDEDNESS: double (D) TOPOLOGY: linear (xi) SEQUENCE DESCRIPTION: SEQ ID NO: 5: GGGGCCCAGT CAGCGTCGAT 20 (2) INFORMATION FOR SEQ ID NO: 6: (l) SEQUENCE CHARACTERISTICS: (A) LENGTH: 70 nucleotides (B) TYPE: nucleic acid (C) STRANDEDNESS: double (D) TOPOLOGY: linear (xi) SEQUENCE DESCRIPTION: SEQ ID NO: 6: AAAAGGAGGA GGCCTTGATA GAGAGGACCT GTTTAAACGT TTAAACGGAT 50 CCTCTTCCTC TTCCTCTTCC 70 (2) INFORMATION FOR SEQ ID NO: 7: (l) SEQUENCE CHARACTERISTICS: (A) LENGTH: 34 nucleotides (B) TYPE: nucleic acid (C) STRANDEDNESS: single (D) TOPOLOGY: linear (xi) SEQUENCE DESCRIPTION: SEQ ID NO: 7: CTAAACCATT GGTATGGGCC AGTGAATTGT AATA 34 (2) INFORMATION FOR SEQ ID NO: 8: (l) SEQUENCE CHARACTERISTICS: (A) LENGTH: 55 nucleotides (B) TYPE: nucleic acid (C) STRANDEDNESS: single (D) TOPOLOGY: linear (xi) SEQUENCE DESCRIPTION: SEQ ID NO: 8: CGCGCAGCCC GCATCGTTTA TGCTACAGAC TGTCAGTGCA 40 GCTCTCCGAT CCAAA 55 (2) INFORMATION FOR SEQ ID NO: 9: (i) SEQUENCE CHARACTERISTICS: (A) LENGTH: 16 nucleotides (B) TYPE: nucleic acid (C) STRANDEDNESS: double (D) TOPOLOGY: linear (xi) SEQUENCE DESCRIPTION: SEQ ID NO: 9: TCGATGGGCT AGATTT 16 (2) INFORMATION FOR SEQ ID NO: 10: (i) SEQUENCE CHARACTERISTICS: (A) LENGTH: 30 nucleotides (B) TYPE: nucleic acid (C) STRANDEDNESS: double (D) TOPOLOGY: linear (xi) SEQUENCE DESCRIPTION: SEQ ID NO: 10: ANNNTACAGC TGCATCCCTT GGCGCTGAGG 30 (2) INFORMATION FOR SEQ ID NO: 11: (i) SEQUENCE CHARACTERISTICS: (A) LENGTH: 30 nucleotides (B) TYPE: nucleic acid (C) STRANDEDNESS: double (D) TOPOLOGY: linear ( i) SEQUENCE DESCRIPTION: SEQ ID NO: 11: NANNTACAGC TGCATCCCTG GGCCTGTAAG 30 (2) INFORMATION FOR SEQ ID NO: 12: (i) SEQUENCE CHARACTERISTICS: (A) LENGTH: 30 nucleotides (B) TYPE: nucleic acid (C) STRANDEDNESS: double (D) TOPOLOGY: linear (xi) SEQUENCE DESCRIPTION: SEQ ID NO: 12: CNNNTACAGC TGCATCCCTT GACGGGTCTC 30 (2) INFORMATION FOR SEQ ID NO: 13: (i) SEQUENCE CHARACTERISTICS: (A) LENGTH: 30 nucleotides (B) TYPE: nucleic acid (C) STRANDEDNESS: double (D) TOPOLOGY: linear (xi) SEQUENCE DESCRIPTION: SEQ ID NO: 13: NCNNTACAGC TGCATCCCTG CCCGCACAGT 30 (2) INFORMATION FOR SEQ ID NO: 14: (i) SEQUENCE CHARACTERISTICS: (A) LENGTH: 30 nucleotides (B) TYPE: nucleic acid (C) STRANDEDNESS: double (D) TOPOLOGY: linear (xi) SEQUENCE DESCRIPTION: SEQ ID NO: 14: GNNNTACAGC TGCATCCCTT CGCCTCGGAC 30 (2) INFORMATION FOR SEQ ID NO: 15: (i) SEQUENCE CHARACTERISTICS: (A) LENGTH: 30 nucleotides (B) TYPE: nucleic acid (C) STRANDEDNESS: double (D) TOPOLOGY: linear (xi) SEQUENCE DESCRIPTION: SEQ ID NO: 15: NGNNTACAGC TGCATCCCTG ATCCGCTAGC 30 (2) INFORMATION FOR SEQ ID NO: 16: (i) SEQUENCE CHARACTERISTICS: (A) LENGTH: 30 nucleotides (B) TYPE: nucleic acid (C) STRANDEDNESS: double (D) TOPOLOGY: linear (xi) SEQUENCE DESCRIPTION: SEQ ID NO: 16: TNNNTACAGC TGCATCCCTT CCGAACCCGC 30 (2) INFORMATION FOR SEQ ID NO: 17: (i) SEQUENCE CHARACTERISTICS: (A) LENGTH: 30 nucleotides (B) TYPE: nucleic acid (C) STRANDEDNESS: double (D) TOPOLOGY: linear (xi) SEQUENCE DESCRIPTION: SEQ ID NO: 17: NTNNTACAGC TGCATCCCTG AGGGGGATAG 30 (2) INFORMATION FOR SEQ ID NO: 18: (i) SEQUENCE CHARACTERISTICS: (A) LENGTH: 30 nucleotides (B) TYPE: nucleic acid (C) STRANDEDNESS: double (D) TOPOLOGY: linear (xi) SEQUENCE DESCRIPTION: SEQ ID NO: 18: NNANTACAGC TGCATCCCTT CCCGCTACAC 30 (2) INFORMATION FOR SEQ ID NO: 19: (i) SEQUENCE CHARACTERISTICS: (A) LENGTH: 30 nucleotides (B) TYPE: nucleic acid (C) STRANDEDNESS: double (D) TOPOLOGY: linear (xi) SEQUENCE DESCRIPTION: SEQ ID NO: 19: NNNATACAGC TGCATCCCTG ACTCCCCGAG 30 (2) INFORMATION FOR SEQ ID NO: 20: (i) SEQUENCE CHARACTERISTICS: (A) LENGTH: 30 nucleotides (B) TYPE: nucleic acid (C) STRANDEDNESS: double (D) TOPOLOGY: linear (xi) SEQUENCE DESCRIPTION: SEQ ID NO: 20: NNCNTACAGC TGCATCCCTG TGTTGCGCGG 30 (2) INFORMATION FOR SEQ ID NO: 21: (1) SEQUENCE CHARACTERISTICS: (A) LENGTH: 30 nucleotides (B) TYPE: nucleic acid (C) STRANDEDNESS: double (D) TOPOLOGY: linear (xi) SEQUENCE DESCRIPTION: SEQ ID NO: 21: NNNCTACAGC TGCATCCCTC TACAGCAGCG 30 (2) INFORMATION FOR SEQ ID NO: 22: (i) SEQUENCE CHARACTERISTICS: (A) LENGTH: 30 nucleotides (B) TYPE: nucleic acid (C) STRANDEDNESS: double (D) TOPOLOGY: linear (xi) SEQUENCE DESCRIPTION: SEQ ID NO: 22: NNGNTACAGC TGCATCCCTG TCGCGTCGTT 30 (2) INFORMATION FOR SEQ ID NO: 23: (i) SEQUENCE CHARACTERISTICS: (A) LENGTH: 30 nucleotides (B) TYPE: nucleic acid (C) STRANDEDNESS: double (D) TOPOLOGY: linear (xi) SEQUENCE DESCRIPTION: SEQ ID NO: 23: NNNGTACAGC TGCATCCCTC GGAGCAACCT 30 (2) INFORMATION FOR SEQ ID NO: 24: (i) SEQUENCE CHARACTERISTICS: (A) LENGTH: 30 nucleotides (B) TYPE: nucleic acid (C) STRANDEDNESS: double (D) TOPOLOGY: linear (xi) SEQUENCE DESCRIPTION: SEQ ID NO: 24: NNTNTACAGC TGCATCCCTG GTGACCGTAG 30 ( 2 ) INFORMATION FOR SEQ I D NO : 25 : (1) SEQUENCE CHARACTERISTICS: (A) LENGTH: 30 nucleotides (B) TYPE: nucleic acid (C) STRANDEDNESS: double (D) TOPOLOGY: linear (xi) SEQUENCE DESCRIPTION: SEQ ID NO: 25: NNNTTACAGC TGCATCCCTC CCCTGTCGGA 30 (2) INFORMATION FOR SEQ ID NO: 26: (1) SEQUENCE CHARACTERISTICS: (A) LENGTH: 78 nucleotides (B) TYPE: nucleic acid (C) STRANDEDNESS: single (D) TOPOLOGY: linear (xi) SEQUENCE DESCRIPTION: SEQ ID NO: 26: ACTAATCGTC TCACTATTTA ATTAANNNNN NNNNNNNNNN 40 NNNNNNNNNN NNNNNNNGGT TTTTTTTTTT TTTTTTTV 78 (2) INFORMATION FOR SEQ ID NO: 27: (1) SEQUENCE CHARACTERISTICS: (A) LENGTH: 17 nucleotides (B) TYPE: nucleic acid (C) STRANDEDNESS: double (D) TOPOLOGY: linear (xi) SEQUENCE DESCRIPTION: SEQ ID NO: 27: ATAGGGGTCT TCGGTAC 17 (2) INFORMATION FOR SEQ ID NO: 28: (l) SEQUENCE CHARACTERISTICS: (A) LENGTH: 19 nucleotides (B) TYPE: nucleic acid (C) STRANDEDNESS: double (D) TOPOLOGY: linear (xi) SEQUENCE DESCRIPTION: SEQ ID NO: 28: GATCAGCTGC TGCAAATTT 19

Claims: We claim 1 A method of determining the nucleotide sequence at an end of a polynucleotide, the method comprising the steps of hgating one or more encoded adaptors to an end of the polynucleotide, each encoded adaptor having an oligonucleotide tag selected from a minimally cross-hybπdizmg set of oligonucleotides and a protruding strand complementary to a portion of a strand of the polynucleotide, and identifying one or more nucleotides m each of said portions of the strand of the polynucleotide by specifically hybridizing a tag complement to each oligonucleotide tag of the one or more encoded adaptors ligated thereto 2 The method of claim 1 wherein said step of hgating mcludes hgating a plurality of different encoded adaptors to said end of said polynucleotide such that said protruώng strands of the plurality of different encoded adapators are complementary to a plurality of different portions of said strand of said polynucleotide such that there is a one-to-one correspondence between said different encoded adaptors and the different portions of said strand 3 The method of claim 2 wherein said different portions of said strand of said polynucleotide are contiguous 4 The method of any of claims 1 to 3 wherein said protruding strand of said encoded adaptors contains from 2 to 6 nucleotides and wherein said step of identifying includes specifically hybridizing said tag complements to said oligonucleotide tags such that the identity of each nucleotide in said portions of said polynucleotide is determined successively 5 The method of any of claims 1 to 4 wherem said step of identifying further includes providing a number of sets of tag complements equivalent to the number of nucleotides to be identified in said portions of said polynucleotide 6 The method of claim 5 wherein said step of identifying further includes providing said tag complements in each of said sets that are capable of indicating the presence of a predetermined nucleotide by a signal generated by a fluorescent signal generating moiety, there being a different fluorescent signal generating moiety for each kind of nucleotide 7 The method of any of claims 1 to 6 wherein said oligonucleotide tags of said encoded adaptors are single stranded and said tag complements to said oligonucleotide tags are smgle stranded such that specific hybridization between an oligonucleotide tag and its respective tag complement occurs through Watson-Cnck base pairing 8 The method of claim 7 wherein said encoded adaptors have the form 5'-p(N) n (N ) r (N ) S (N ) q (N ) t -3' z(N') r (N') s (N') q -5' or p(N ) r (N ) S (N ) (N ) t -3' 3'-z(N) n (N') r (N') s (N') q -5 » where N is a nucleotide and N' is its complement, p is a phosphate group, z is a 3' hydroxyl or a 3' blocking group, n is an integer between 2 and 6, mclusive, r is an integer between 0 and 18, inclusive, s is an mteger which is either between four and six, mclusive, whenever the encoded adaptor has a nuclease recogmtion site or is 0 whenever there is no nuclease recognition site, q is an mteger greater than or equal to 0, and t is an integer greater than or equal to 8 9 The method of claim 8 wherein r is between 0 and 12. inclusive, t is an mteger between 8 and 20, inclusive, and z is a phosphate group 10 The method of any of claims 1 to 6 wherein said oligonucleotide tags of said encoded adaptors are double stranded and said tag complements to said oligonucleotide tags are single stranded such that specific hybridization between an oligonucleotide tag and its respective tag complement occurs through the formation of a Hoogsteen or reverse Hoogsteen tnplex 11 The method of claim 10 wherein said encoded adaptors have the form 5'-p(N) n (N ) r (N ) έ (N ) (N ) t -3' z(N') r (N') s (N*) q (N ) t -5* or p(N ) r (N ) S (N ) (N ) t -3' 3'-z(N) n (N , ) r (N , ) s (N')„(N ) -5' where N is a nucleotide and N' is its complement, p is a phosphate group, z is a 3' hydroxyl or a 3' blocking group, n is an integer between 2 and 6, inclusive, r is an integer between 0 and 18, inclusive, s is an mteger which is either between four and six, inclusive, whenever the encoded adaptor has a nuclease recognition site or is 0 whenever there is no nuclease recognition site, q is an integer greater than or equal to 0, and t is an integer greater than or equal to 8 12 The method of claim 1 1 wherein r is between 0 and 12, inclusive, t is an mteger between 12 and 24, inclusive, and z is a phosphate group 13 The method of any of claims 1 to 12 wherein members of said minimally cross- hybndiz g set differ from every other member by at least six nucleotides 14 A method of determining the nucleotide sequences of a plurality of polynucleotides, the method compnsmg the steps of (a) attaching a first oligonucleotide tag from a repertoire of tags to each polynucleotide m a population of polynucleotides such that each first oligonucleotide tag from the repertoire is selected from a first minimally cross-hybndizing set, (b) sampling the population of polynucleotides to form a sample of polynucleotides such that substantially all different polynucleotides in the sample have different first oligonucleotide tags attached, (c) sorting the polynucleotides of the sample by specifically hybndizmg the first oligonucleotide tags with their respective complements, the respective complements bemg attached as uniform populations of substantially identical oligonucleotides m spatially discrete regions on the one or more solid phase supports, (d) hgating one or more encoded adaptors to an end of the polynucleotides in the sample, each encoded adaptor having a second oligonucleotide tag selected from a second minimally cross-hybndizing set and a protruding strand complementary to a protrudmg strand of a polynucleotide of the population, and (e) identifying a plurality of nucleotides m said protrudmg strands of the polynucleotides by specifically hybndizmg a tag complement to each second oligonucleotide tag of the one or more encoded adaptors 15 The method of claim 14 further mcludmg the steps of (f) cleavmg said encoded adaptors from said polynucleotides with a nuclease having a nuclease recognition site separate from its cleavage site so that a new protrudmg strand is formed on said end of each of said polynucleotides, and (g) repeating steps (d) through (f) 16 A method of identifying a population of mRNA molecules, the method compnsmg the steps of (a) forming a population of cDNA molecules from the population of mRNA molecules such that each cDNA molecule has a first oligonucleotide tag attached, the first oligonucleotide tags bemg selected from a first mmimally cross-hybndizing set, (b) sampling the population of cDNA molecules to form a sample of cDNA molecules such that substantially all different cDNA molecules have different first oligonucleotide tags attached, (c) sorting the cDNA molecules by specifically hybndizmg the first oligonucleotide tags with their respective complements, the respective complements bemg attached as umform populations of substantially identical complements m spatially discrete regions on one or more solid phase supports, (d) gat g one or more encoded adaptors to an end of the cDNA molecules in the population, each encoded adaptor havmg a second oligonucleotide tag selected from a second minimally cross-hybndizing set and a protruding strand complementary to a protruding strand of a cDNA molecule of the sample, and (e) determining the identity and ordenng of a plurality of nucleotides in each of said protruding strands of the cDNA molecules by specifically hybndizmg a tag complement to each second oligonucleotide tag of the one or more encoded adaptors, wherein the population of mRNA molecules is identified by the frequency distnbution of the portions of sequences of the cDNA molecules 17 The method of claim 16 further including the steps of (f) cleavmg said encoded adaptors from said polynucleotides with a nuclease having a nuclease recognition site separate from its cleavage site so that a new protruding strand is formed on said end of each of said cDNA molecules, and (g) repeating steps (d) through (f) 18 A method of determining the nucleotide sequence at an end of a polynucleotide, the method compnsmg the steps of (a) hgatmg an encoded adaptor to an end of the polynucleotide, the encoded adaptor havmg an oligonucleotide tag selected from a minimally cross-hybndizmg set of oligonucleotides and a protruding strand complementary to a portion of a strand of the polynucleotide, (b) identifying one or more nucleotides in the portion of the strand of the polynucleotide by specifically hybndizmg a tag complement to the oligonucleotide tag of the encoded adaptor ligated thereto, (c) cleavmg the encoded adaptor from the end of the polynucleotide with a nuclease having a nuclease recogmtion site separate from its cleavage site so that a new protruding strand is formed at the end of the polynucleotide, and (d) repeatmg steps (a) through (c) 19 The method of claim 18 wherein said protrudmg strand of said encoded adaptor contains from 2 to 6 nucleotides and wherein step of identifying includes specifically hybndizmg successive said tag complements to said oligonucleotide tag such that the identity of each nucleotide in said portion of said polynucleotide is determined successively 20 The method of claim 18 or claim 19 wherein said step of identifying further mcludes providing a number of sets of tag complements equivalent to the number of nucleotides to be identified m said portion of said polynucleotide 21 The method of claim 20 where said step of identifying further includes providing said tag complements in each of said sets that are capable of indicating the presence of a predetermined nucleotide by a signal generated by a fluorescent signal generating moiety, there being a different fluorescent signal generating moiety for each kind of nucleotide 22 The method of any of claims 18 to 21 wherem said oligonucleotide tags of said encoded adaptors are smgle stranded and said tag complements to said oligonucleotide tags are smgle stranded such that specific hybndization between an oligonucleotide tag and its respective tag complement occurs through Watson-Cnck base pairing 23 A composition of matter compnsmg a double stranded oligonucleotide adaptor having the form 5'-p(N) n (N ) r (N ) S (N ) (N ) t -3' z(N') r (N') s (N') q -5' or p(N ) r (N ) S (N )q(N 3'-z(N) n (N' ) r (N') s N') q -5' where N is a nucleotide and N' is its complement, p is a phosphate group, z is a 3' hydroxyl or a 3' blocking group, n is an mteger between 2 and 6, mclusive, r is an integer between 0 and 18, inclusive, s is an mteger which is either between four and six, mclusive, whenever the encoded adaptor has a nuclease recognition site or is 0 whenever there is no nuclease recognition site, q is an integer greater than or equal to 0, t is an integer greater than or equal to 8 24. The composition of claim 23 wherein r is between 0 and 12, inclusive, t is an integer between 8 and 20, inclusive, z is a phosphate group, and said single stranded moiety (N) t is a member of a minimally cross-hybridizing set. 25. A composition of matter comprising a double stranded oligonucleotide adaptor having the form: 5'-p(N) n (N ) r (N ) S (N )q(N ) f-3 z(N') r (N') s (N') q (N') t -5' or p(N ) r (N ) S (N ) q (N ) t -3' 3 , -z(N) n (N') r (N') s (N*) q (N') t -5' where N is a nucleotide and N' is its complement, p is a phosphate group, z is a 3' hydroxyl or a 3' blocking group, n is an integer between 2 and 6, inclusive, r is an integer between 0 and 18, inclusive, s is an integer which is either between four and six, inclusive, whenever the encoded adaptor has a nuclease recognition site or is 0 whenever there is no nuclease recognition site, q is an integer greater than or equal to 0, and t is an integer greater than or equal to 8. 26. The composition of claim 25 wherein r is between 0 and 12, inclusive, t is an integer between 12 and 24, inclusive, z is a phosphate group, and said double stranded moiety -(N ) t -(N')t is a member of a minimally cross-hybridizing set. 27. The composition of any of claims 23 to 26 wherein n equals 4 and wherein members of said minimally cross-hybridizing set differ from every other member by at least six nucleotides.

Inventors: ALBRECHT GLENN, BRENNER SYDNEY, DUBRIDGE ROBERT B, LLOYD DAVID H, PALLAS MICHAEL C, ALBRECHT, GLENN, BRENNER, SYDNEY, DUBRIDGE, ROBERT, B., LLOYD, DAVID, H., PALLAS, MICHAEL, C.
Applicants: LYNX THERAPEUTICS INC, LYNX THERAPEUTICS, INC.
Application year: 1997
Main classification: C12Q1
IPC codes: C12N15, C12Q1, G06F17