Abstract:
Disclosed is the use of artificially-generated nucleic acid coded markers to monitor nucleic acid amplification and sequencing reactions designed to detect or analyze biological samples. The markers generally include, along with a unique sequence preferably including coded section designed to represent one or more factors of interest, primer annealing sequences so that the marker may be amplified and sequenced in the same process and using the same amplification and sequencing primers as for the sample target. The invention also relates to the marker itself, and other uses, such as identifying the origin of various materials or products.

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
       [0001]    This application is a divisional of U.S. patent application Ser. No. 11/481,046, filed Jul. 6, 2006, now allowed, which claims priority to provisional Application Ser. No. 60/696,824, filed Jul. 7, 2005. 
     
    
     SUBMISSION OF SEQUENCE LISTING ON ASCII TEXT FILE 
       [0002]    The content of the following submission on ASCII text file is incorporated herein by reference in its entirety: a computer readable form (CRF) of the Sequence Listing (file name: 717482000310SeqList.txt, date recorded: Jul. 2, 2014, size: 4,253 bytes). 
       BACKGROUND OF THE INVENTION 
       [0003]    1. Field of the Invention 
         [0004]    This invention relates to the analysis or identification of biological samples using nucleic acid detection techniques, such as DNA amplification and sequencing. More particularly, the invention relates to ways of monitoring problems that can arise during such techniques, such as cross-contamination of materials from different sources, as well as enabling sample traceability and providing internal controls for such techniques. 
         [0005]    2. Background Art 
         [0006]    The technology of molecular biology has opened up number of applications for testing, analysis and diagnosis using nucleic acid techniques (see References 1, 2 and 3 of the References section below). This includes routine testing of clinical, veterinary, and plant samples, as well as development of drugs and specialty bio-pharmaceuticals. 
         [0007]    In the early 1990s, a novel nucleic acid amplification technology, polymerase chain reaction (PCR), was made possible. Although the primary use of this technology was targeted at making millions of copies of DNA segments that could be cloned, PCR was later adopted in routine nucleic acid testing, e.g. testing for the presence of infectious microorganisms or specific genes or mutations. Presently, there are number of available assays that use conventional PCR as well as other modifications, such as reverse transcriptase PCR (RT-PCR, used to amplify sequences derived from RNA), ligase chain reaction (LCR), transcription mediated amplification (TMA), etc, to enable the amplification of target nucleic acid molecules having sequences of interest. In addition to target amplification technologies, there are number of signal amplification technologies, such as b-DNA and hybrid capture technology that are presently being used in routine testing. The use of nucleic acids techniques has made routine testing faster so that results can be obtained within hours rather than waiting days or weeks for bacterial cultures to grow. 
         [0008]    Whatever the specific technology, routine testing warrants sensitivity (confidence that a negative is true negative) and specificity (confidence that a positive is a true positive). For example, nucleic acids based technologies have to conform to sensitivity and specificity requirements dictated by controlling authorities such as CLIA (Clinical laboratory Improvement Amendment, USA). In addressing these requirements, it has become routine to include, in each batch of testing, one sample without a target that would serve as negative control and one sample with the target as a true positive control, but this increases the complexity and cost of the testing operation. Furthermore, the controls may not be subjected to exactly the same conditions and environment as the actual samples. 
         [0009]    Moreover, the fact that extremely small amounts of DNA or RNA may be amplified by PCR and similar technologies means that there is a real possibility of contamination of the samples (i.e., with amplified foreign DNA) employed for testing because small amounts of contaminants may also be amplified and yield an inaccurate result. 
         [0010]    Also there is a need for traceability of samples because large numbers of samples are routinely tested and can easily be mixed up. Such sample mix-ups sometimes occur in hospitals and laboratories, so there is also a need for a way of confirming the origin or identity of a particular sample even if there is no contamination as such. 
         [0011]    Additionally, ingredients in certain samples (e.g. urine) are known to inhibit target amplification processes, such as PCR or RNA polymerization (References 6 and 7), so there is a need to ensure that there are no inhibitory substances in the samples that could have that effect. In addressing the inhibitory substance issue in the past, artificial targets have been introduced into the samples where the artificial targets will have the same annealing site as that of the target, and the artificial targets produce an amplicon that carries an internal sequence that is different from that of the target (References 4 and 5). Using a third probe specific to this target will detect the artificial target ensuring there are no inhibitory substances. However, this procedure is quite complicated and may not always be reliable. 
         [0012]    There is therefore a need for an improved means of monitoring nucleic acid testing techniques. 
       SUMMARY OF THE INVENTION 
       [0013]    One exemplary form of the invention provides a method of testing for the presence of a target nucleic acid in a sample, which method comprises providing amplification primers designed to anneal to the target nucleic acid flanking a characteristic sequence thereof, carrying out a nucleic acid amplification procedure employing the primers to produce an amplicon containing the characteristic sequence, providing a sequencing primer designed to anneal at or adjacent to the characteristic sequence of the amplicon, and sequencing at least part of the characteristic sequence to confirm the presence the target nucleic acid in the sample, wherein a marker is amplified and sequenced as a control at the same time under identical conditions using identical amplification and sequencing primers, the marker having a unique nucleotide sequence flanked by annealing sites for the amplification and sequencing primers. 
         [0014]    The unique sequence preferably comprises a coding region of nucleic acid bases that encodes specific information according to a predetermined code. 
         [0015]    Another exemplary embodiment provides a method of carrying out a test for a target nucleic acid sequence in a sample, which method comprises carrying out a nucleic acid amplification procedure designed to produce amplicons containing a characteristic part of the target sequence, if present in the sample, and carrying out a sequencing procedure designed to reveal the presence of amplicons containing the characteristic part, thereby confirming the presence of the target nucleic acid in the sequence, wherein the results of the sequencing procedure are also investigated for indication of the presence of amplicons containing a pre-determined coded sequence from one or more artificial markers, and, if found, decoding the coded sequence(s) to obtain information contained in the marker(s). 
         [0016]    The artificial marker may be added to the sample prior to carrying out the nucleic acid amplification and sequencing steps, thus forming an internal marker, and may include, in addition to the coded sequence, nucleic acid sequences that allow amplification and sequencing of the coded sequence simultaneously with amplification and sequencing of the characteristic part of the target nucleic acid sequence. 
         [0017]    Another exemplary embodiment of the invention provides a method of testing for the presence of a target nucleic acid sequence in a sample, which method comprises providing amplification primers designed to anneal to the target nucleic acid flanking a characteristic part thereof, carrying out a nucleic acid amplification procedure employing the primers to produce an amplicon containing the characteristic part of the target nucleic acid sequence if the sequence is present in the sample, and sequencing at least part of the amplicon if thereby produced to reveal the characteristic part of the target nucleic acid sequence, wherein a marker is introduced into the sample prior to the amplification procedure, the marker having a unique nucleotide coding sequence encoding specific information flanked by nucleotide sequences that permit the coding sequence also to be amplified and sequenced as the characteristic part of the target is amplified and sequenced, thereby revealing the specific information corresponding to the coding sequence as well as the presence or absence of the target nucleic acid sequence in the sample. 
         [0018]    Preferably, the nucleic acid amplification procedure involves polymerase chain reaction and the nucleotide sequences that permit the coding sequence to be amplified include sequences that anneal to primers used for the amplification of the target sequence. 
         [0019]    Another exemplary form of the invention provides a method of enabling positive identification of an item, which comprises adding to the item a marker including a coded nucleic acid sequence containing information about the item, and sequences that permit amplification and sequencing of the coded nucleic acid sequence. 
         [0020]    Another exemplary form of the invention provides a marker comprising a molecule including a nucleic acid sequence, the sequence comprising an artificial coding sequence that may be decoded to reveal specific information, and regions that permit amplification and sequencing of the coding sequence. 
         [0021]    Preferably, the invention uses coded artificially-generated nucleotide sequences in the same assay as a target sample to (a) detect cross-contamination if it occurs, (b) trace the origin of samples, and/or (c) ensure that there are no inhibitory substances in the assay. 
         [0022]    The invention may also be applied to the detection of trace contamination in other processes as well as processing equipment such as Tripath® thin preparation, and may also be employed during the manufacture of biopharmaceuticals, validating filtration (filter validation), and the like. 
         [0023]    The term “amplicon” as used herein means a molecule or collection of molecules (population) obtained by amplifying a particular nucleic acid sequence by a nucleic acid amplification technique, e.g. PCR or RT-PCR. 
         [0024]    The invention may be used in the following ways (among others). 
       Cross-Contamination 
       [0025]    During DNA-based amplification technologies, in particular, cross-contamination of a sample may occur at any stage of the procedure, for example, as follows:
       A target from another sample may be accidentally introduced as a cross-contaminant.   An inhibitory substance from another sample may be introduced as a cross-contaminant.   There may be a general contamination at the site of sample collection (e.g., in the laboratory or at physician&#39;s office, etc.).   The reagents that are used in the assay may be contaminated with target(s).   The consumables used in the assay could be contaminated with the target(s).   Samples may be contaminated on receiving and initial processing at a laboratory.   Samples may be contaminated during processing particularly using 96-well plates.       
 
         [0033]    Presently there are no sensitive methods that can detect these cross-contaminations. The present invention provides a technique that can detect cross-contamination. It does not prevent cross-contamination, but it enables it to be detected if it does occur. 
         [0034]    If there is cross-contamination of samples, the artificial codes of two or more markers will be revealed instead of just one, and the information in the markers can be used to reveal where the cross-contamination came from. 
       Traceability 
       [0035]    If a sample containing a marker is of unknown origin, the sample may be amplified and sequenced and, if the artificial code of the marker is thereby revealed, the information in it will reveal the source and details of the sample (depending on the information encoded into the coding sequence). 
         [0036]    The processing of large numbers of samples is a challenge, especially during routine testing. Sample mix-up is one of the common errors in routine testing. Although external identification systems, such as bar code identification, etc., are commonly employed, they are still subject to human and/or mechanical error. The present invention provides a built-in nucleotide sequence based coding sequence that may identify, for example, the customer, type of sample (urine or swab), test requested (e.g.,  Chlamydia trachchomatis  and  Neisseria gonorrhea ), well-position in the testing equipment or 8 well strip or 96 or 384 well plate, etc. 
       Inhibitory Substances 
       [0037]    If a marker according to the invention is added to a sample that may contain inhibitory substances and the usual amplification and sequencing is performed, the presence of amplicons containing the coding sequence will show that the amplification and sequencing procedures were not inhibited by any substance present. The absence of amplicons containing the sample sequence will then show conclusively that the expected target DNA or RNA was not present in the sample. Alternatively, the absence of the artificial sequence, will show that the amplification and sequencing was inhibited. 
         [0038]    The invention has the advantage that the marker molecule and the sample molecule are subjected to exactly the same environment and procedures, so the results are highly reliable. 
       Construct of the Control Target 
       [0039]    The marker molecule may be constructed and encoded to have, for example, the following potential uses: 
         [0040]    Traceability:
       customer Identification sequence   sample type identification sequence   test identification sequence       
 
         [0044]    Cross-Contamination/Traceability:
       well identification sequence       
 
         [0046]    Internal Positive Control
       PCR primer annealing sequences   Sequencing primer annealing sequences       
 
         [0049]    Ideally, the coding sequence of the marker will have the sequence codes flanked by both the upstream and the downstream target amplification primers, as well as including an annealing site for the sequencing primer that is designed for the sample target molecule. Use of such a marker will not only insure that the PCR primers are annealing to the sample target in the sample conditions, but also that the PCR process is not inhibited. Similarly, the sequencing primer anneals both to amplicons produced from the sample target as well as amplicons produced from the marker, and confirms that the polymerization required for sequencing is not inhibited in both the target and the marker. 
         [0050]    Markers having different codes may be used either separately as independent batch controls in separate wells, or, more preferably, mixed with the clinical samples as internal controls for each sample. When the marker is used in combination with clinical samples as an internal control, the construct will preferably have a homogenous nucleotide sequence (e.g. polyA, polyG, polyT or polyC) preceding the first coding cluster (e.g. the customer identification sequence). The length of the homogenous nucleotide sequence will preferably be longer than the target sequence that will be produced by the sequencing primer annealing to the test target from the clinical sample. 
       Coding Sequence 
       [0051]    In one form of the invention, the marker merely includes a unique sequence of bases that distinguishes the marker amplicon from that of the sample target. This is the simplest form of code merely identifying the sequence as belonging to the marker and not to the target nucleic acid. More preferably, however, the marker includes (as said unique sequence or part thereof) a more complex coding region in which nucleotide bases are used as coding symbols to represent any of a number of parameters associated with routine testing. This could involve nucleotides present in DNA, RNA or a combination or modification of these nucleotides. 
         [0052]    The coding region may contain, for example, nucleotide sequences incorporating specific codes for one or numerous factors. Typical factors include codes for: 
         [0053]    i. Customer (e.g. Name of a hospital) 
         [0054]    ii. Sample type (Swab or urine) 
         [0055]    iii. Test ordered ( Chlamydia trachomais, Neisseria gonorrhea ) 
         [0056]    iv. Position in a 96 well plate. 
       Analysis 
       [0057]    The combination of a coded marker and target sequence subjected to amplification and sequencing will generate two groups of truncated polynucleotide chains, i.e. 
         [0058]    a. One generated from the sequencing primer annealing to the test target in the clinical sample. This will normally generate a short (25-35 base) target-specific nucleotide and the nucleotide sequence of the downstream PCR primer. 
         [0059]    b. One generated from the sequencing primer annealing to the marker target will produce a nucleotide sequence preferably starting with a polynucleotide followed by the other elements of the control construct, including the coding region, and the nucleotide sequence of the downstream PCR primer. 
         [0060]    In the absence of expected target from the clinical sample, only the nucleotide sequence generated by the sequencing primer annealing to the control target will be observed. 
         [0061]    If an expected test target is present in the clinical sample, then both A and B will be present and sequences from both will be generated. The observed electropherogram will have a signal overlap in the initial section of sequence read followed by a clear signal. The overlap section will have the test target specific sequence and the downstream PCR primer generated by the sequencing primer annealing to the true positive target in the sample that overlaps with the polynucleotide sequences generated by the same sequencing primer annealing to the control target. In order to analyze the electropherogram, the channel corresponding to the homonucleotide sequence (e.g., poly A, etc.) will be turned off on the sequencing machine and the target sequence will be analyzed (homology matching) using the sequence based on the remaining three nucleotides. 
         [0062]    The distal part of the electropherogram will then be mainly from the truncated molecules generated by the sequencing primer annealing to the marker. Since the distal part of the electropherogram will not have any overlap, all four channels may be turned on for analysis of the nucleotide sequences produced from the marker. 
         [0063]    It should be noted that the present invention may be used in combination with the technology disclosed in U.S. Pat. No. 6,197,510 issued on Mar. 6, 2001 to Thuraiayah Vinaygamoorthy (the disclosure of which is incorporated herein by reference) and referred to by the trademark MultiGEN® (see also Ref 8). This is a platform technology that allows for simultaneous determination of nucleotide sequences from multiple genomes or multiple segments from the same genome or a combination of both. This technology mainly involves three steps: 
         [0064]    (a) Preparation of total nucleic acid from the sample (this could be nucleic acids, RNA, or both); 
         [0065]    (b) Simultaneous amplification of all target genomes (this can be carried out by any suitable target amplification method including PCR), and 
         [0066]    (c) Simultaneous sequencing at the 3′-end of all amplicons. 
         [0067]    The sequences generated may be identified by a BLAST search. The test protocol will vary based on the type of genomic targets to be analyzed (nucleic acid, RNA, or both), the number of targets (2-20 are feasible), and the expected copy number of the targets in the samples. The present invention may be used in this technology by introducing the marker into the sample and amplifying and sequencing the resulting amplicon along with the others produced from the numerous genomes. 
         [0068]    Apart from use in routine testing, this invention also can be used in securing and traceability of valuable items such as, painting, jewels, and paper and other documents. This can be achieved simply by incorporating a marker according to the invention into the item, the marker encoding information about the item. Amplification and sequencing will then reveal the encoded information when required. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0069]      FIG. 1  is a diagram illustrating one preferred way of constructing a marker according to one form of the present invention; 
           [0070]      FIG. 2  is a diagram illustrating a preferred way of carrying out one of the steps of  FIG. 1 ; 
           [0071]      FIG. 3  is a diagram illustrating an alternative to the step of  FIG. 2 ; 
           [0072]      FIG. 4  is a table showing an example of nucleotide sequence based coding system that may be used to incorporate information into a marker molecule; 
           [0073]      FIG. 5  is a diagram illustrating the amplification and sequencing of a marker according to one preferred form of the present invention; 
           [0074]      FIG. 6  is a diagram illustrating simultaneous amplification and sequencing of a marker and a target genome sequence according to one is preferred form of the invention, item  40  show the overlap between the expected target sequence (SEQ ID NO. 15) and the expected sequence from the artificial construct (SEQ ID NO. 16); 
           [0075]      FIG. 7  is a diagram showing three marker constructs and target genomes intended for use when three target genomes are tested simultaneously and genotyping using STRs is also carried out; and 
           [0076]      FIG. 8  is a diagram similar to  FIG. 7  showing alternative marker constructs. 
       
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
       [0077]    The present invention, at least in one preferred form, makes use of the genetic code (the sequence of As, Cs, Ts, Gs, Us representing the bases present in nucleic acids, i.e. adenine, cytosine, tyrosine, guanine and uracil, respectively) to create predetermined unique artificial codes (i.e. unique short sequences that are not likely to be encountered in sample targets that will undergo testing) that can be used as identifiers (sometimes referred to as “signatures”) of materials of a particular kind, origin or treatment. The invention also preferably provides a means by which the code can be multiplied and revealed. 
         [0078]    Short stretches of artificial DNA or RNA (e.g. up to 100 nucleotides) are routinely synthesized by nucleic acid polymerization methods, e.g. for the preparation of primers used for PCR procedures, so such short stretches can be made to have any desired sequence of the “letters” of the genetic code (i.e. a coding sequence forming a coding region of the artificial molecule), and particular combinations of those letters can be designated to have particular meanings. The artificial sequence (coding region) may then be flanked by amplification primer annealing sequences (e.g. for upstream and downstream PCR primers), i.e. by short stretches of nucleic acids having sequences that will anneal with primers designed for subsequent nucleic acid sample amplification and sequencing procedures intended for sample identification. The resulting artificial sequences (preferably also provided with restriction enzyme recognition sites, e.g. Ecor1, HindIII or BamHI, etc., flanking the other sequences) may then be incorporated into DNA or RNA constructs (vectors) using cloning techniques to create double stranded markers that may be added to samples or sample wells, or used as controls. When such a marker is present in a sample and the sample is subjected to amplification and sequencing of a characteristic portion of a sample DNA or RNA, the marker sequence is also amplified and sequenced at the same time. The sequencing procedure reveals the coded region which may then be decoded (by reference to the original code either manually or by computer), and the information thereby obtained may be used for testing, identification or control purposes. The sequencing procedure normally makes use of a sequencing primer and the invention provides a corresponding annealing site for the proposed sequencing primer upstream of the coding sequence. 
         [0079]    By making the PCR primer annealing sites and the sequencing primer annealing sites of the marker correspond to (i.e. anneal to) the primers intended for target sample testing, the present invention, at least in one preferred form, allows both the genomic sequence of the target and the coding region of the marker to be amplified and sequenced at the same time, under the same conditions, and in the same solution and equipment. The coded information can then be used to derive information about the sample sequence or other conclusions of interest. 
         [0080]    The techniques involved in PCR, RT-PCR and nucleic acid sequencing are well known and are disclosed, for example, from: Molecular Cloning: A Laboratory Manual, by Sambrook and Russel, 3rd Edition, Cold Spring Harbor Laboratory Press, 2001 (the disclosure of which is incorporated herein by reference). 
         [0081]    Details of cycle sequencing are also disclosed, for example, in Hisashi Yamakawa and Osamu Ohara, “A DNA Cycle Sequencing Reaction that Minimizes Compressions on Automated Fluorescent Sequencers”,  Nucleic Acid Research , Vol. 25, No. 6, pp. 1131-1312, the disclosure of which is also incorporated herein by reference). 
         [0082]    Briefly stated, in chain terminator sequencing (Sanger sequencing), nucleic acid extension is initiated at a specific site on the substrate DNA acting as a template by using a short oligonucleotide “sequencing primer” complementary to the template at that site. The oligonucleotide primer is extended using a DNA polymerase in the presence of the four deoxynucleotide bases (DNA building blocks), along with a low concentration of a chain terminating nucleotide (most commonly a dideoxynucleotide). The primer or, more commonly in dye termination sequencing, the dideoxynucleotides, are provided with a fluorescent tag (e.g. a fluorescent tag having a different wavelength representing each base). As the DNA strand is elongated, the DNA polymerase catalyses the joining of deoxynucleotides to the corresponding bases. However, if a dideoxynucleotide is joined to a base, then that fragment of DNA can no longer be elongated since a dideoxynucleotide lacks a crucial 3′-OH group. Fragments of all sizes are obtained due to the randomness of the addition of the dideoxynucleotides. The DNA is then denatured and the resulting fragments are separated (with a resolution of just one nucleotide) by gel electrophoresis, from longest to shortest, in a slab polyacrylamide gel, or more commonly, in a narrow glass tube (capillary) filled with a viscous polymer (e.g. POP 7® polymer, Applied Biosystems, USA). The fluorescent signals may then be read simultaneously with a four-channel wavelength detection device (e.g. an ABI PRISM® 3100 Genetic Analyzer capillary gel electropherometer), and the resulting peaks represent individual nuceleotides of one of the four kinds. 
         [0083]    Further details of preferred ways in which preferred forms of the present invention may be carried out and employed are provided below with reference is made to the accompanying drawings. 
         [0084]      FIG. 1  is a diagram providing an overview of a preferred procedure for making a marker according to the invention. First of all, a double-stranded construct  10  is produced. The easiest way to do this is to prepare two single stranded artificial construct parts  11  and  12  each with sequence regions that anneal together so that each part may be extended with sequences complementary to the other using chain extension techniques (the nature of the construct will be explained in more detail later). The double stranded construct  10  is then ligated into a linearized plasmid vector  13  and re-circularized (e.g., using the methods of TOPO® TA cloning, Invitrogen, USA). The resulting vector  14  is introduced into a cell of, for example,  E. coli  strain JM 101 or One Shot® Chemically Competent TOP10  E. coli , using standard cloning techniques and grown with corresponding antibiotic selection. 
         [0085]    The resulting double stranded marker may be used in the form of cells  15  of the organism containing the plasmid incorporating the construct, in the form of the isolated and purified plasmids  16  themselves, or in the form of the digested part  17  of the plasmid containing the construct with the coding elements. 
         [0086]      FIG. 2  shows in more detail one of several preferred ways of making the artificial construct. Using known DNA synthesizing techniques, two construct parts may be formed, each, for example, of approximately 70 mer in length (using the methods of Integrated DNA Technologies, USA, for example). One part  11  (as shown at the upper left hand side of  FIG. 2 ) may consist (in order from the 5′-end), of an EcoR1 recognition site  18 , an upstream PCR primer binding site  19 , and a sequencing primer binding site  20 , which sites may be separated by unspecified DNA  21 . The second construct part  12  may consist (from the 3′-end) of the complement  20 ′ to the sequencing binder site, a coding region  22 , a downstream PCR primer binding site  23  and an EcoR1 site  24 . As shown in  FIG. 2 , a double stranded construct  10  contains the EcoR1 recognition site  18 , the upstream PCR primer binding site  19 , the sequencing primer binding site  20 , a complement  22 ′ to the coding region  22 , a complement  23 ′ to the downstream PCR primer binding site  23  and a complement  24 ′ to the EcoR1 site  24 . The complementary strand contains a complement  18 ′ to the EcoR1 recognition site,  18 , a complement  19 ′ to the upstream PCR primer binding site, a complement  20 ′ to the sequencing primer binding site, the coding region  22 , the downstream PCR primer binding site  23  and an EcoR1 site  24 . 
         [0087]    When mixed together under annealing conditions, the construct parts will anneal at the sequencing binder site  20 ,  20 ′, and the annealed construct can be chain-extended in the direction of the arrows as shown using known methods to produce a double-stranded DNA molecule  10  with each part having the full length and complementary sequences. 
         [0088]    Of course, it is not essential to use the amplification primer sites or the sequencing primer site as the annealing regions for the two construct parts  11  and  12  because any mutually complementary region of the primers could be designed for this purpose. 
         [0089]    When the resulting marker containing these sequences is amplified by PCR, an amplicon will be generated that will have PCR primer sequences at both ends with a sequencing primer in between and the coding sequence between the sequencing primer and one of the PCR primers. 
         [0090]      FIG. 3  shows a modification of the procedure of  FIG. 2 , where the first construct part  11  contains virtually the whole of the construct sequence and the second part  12  just comprises the downstream PCR binder site  23  and the EcoR1 site  24 , but again the double stranded construct is produced by chain extension in the direction of the arrow as shown. 
         [0091]    As already noted, in the coding region  22 , nucleotides are used as coding symbols to represent any of a number of parameters associated with routine testing. 
         [0092]    The variables may be coded using either: 
         [0093]    i. one nucleotide e.g. A 
         [0094]    ii. two nucleotides e.g. AA 
         [0095]    iii. three nucleotides e.g. AAA 
         [0096]    iv. or any number of nucleotides, e.g. AAAAAAAA 
         [0097]    v. any combination of nucleotides, e.g. ATG or ATTGT. 
         [0098]    Of course, the higher the number of nucleotides used for a specific factor, the greater the amount of information that may be included (the use of a single nucleotide, for example, would enable the coding of only four pieces of information represented by the bases A, C, T (U) or G. 
         [0099]    The letters may be spaced along the coding sequence in clusters representing different factors or kinds of information, if necessary separated by recognizable spacers (e.g. a cluster of three or more identical letters). The position of a cluster along the coding sequence may be used to identify the factor that a particular cluster represents (e.g., in the 5′ to 3′ direction, first comes the customer identification cluster, then the type of sample cluster, etc. 
         [0100]    An example of a code that may be incorporated into a coding region is shown in the table of  FIG. 4 . The full coding sequence will be a combination of the sequence parts (clusters) shown in the table. For example, a first part of the artificial sequence (i.e. first cluster of nucleotides) may identify a particular client (person or organization that supplies samples) and this may be, for example, the sequence ATGTCC as shown (a different unique sequence would be used for a different client). There may then be sequences intended to identify a particular type of sample, i.e. a swab (ATATA) or urine (GTGTGT), what the test is intended to find (Gonorrhea/ Chlamydia -GCGCGC), the row of the plate (one of the 12 sequences shown for a common 96-well plate), and there may be a spacer sequence (e.g. TTT) intended to show the start and end of one or more of the other sequence clusters). A specific sequence for a particular marker might then be as follows: 
         [0000]                            (SEQ ID, No: 1)           ATGTC CTTTATATATTTGC GCG CTTTAAACCCTTTGGGAAAA             
which would indicate a particular client with a sample from a swab being tested for gonorrhea and inserted into a well in row 1 of a 96-well plate.
 
         [0101]    The coding sequence above may also be provided with a lead-in sequence designed merely to make the resulting amplicon larger (of greater length) so that results obtained during sequencing will not overlap with those from the amplicon derived from the sample sequence (see later). For example, the coding sequence may be provided with an homogeneous sequence, such as a 27 mer poly-A lead-in sequence. 
         [0102]    As shown in  FIGS. 2 and 3 , the coding sequence will then be flanked by sequences that will anneal to upstream and downstream PCR primers intended for use with the sample tests (e.g. intended to amplify and sequence a section of the genome of the organism that produces gonorrhea) and also a sequence that will anneal to a sequencing primer also intended for the sample tests. 
         [0103]    In use, such a construct, when amplified and sequenced, will reveal a sequence  30  as shown in  FIG. 5 . The information in the sequence can then be decoded (either manually or automatically using a computer) from a table such as the one shown in  FIG. 4 . 
         [0104]    The events that will take place when both a marker and a target are present in the sample are represented in  FIG. 6 . It should be noted that, in this figure, the coding region of the marker is different from that shown in  FIG. 5  and disclosed above. In STEP  1  as shown, PCR primers  32  and  33  added to the sample to produce amplification of the sample target sequence  35  also produce amplification of the artificial marker  36 . As shown in STEP  2 , sequencing primer  37  added for cycle sequencing of the sample target amplicon (left-hand side) will also result in sequencing of the artificial marker amplicon (right-hand side). The expected target sequence (SEQ ID NO: 15) and the expected sequence from the artificial marker construct (SEQ ID NO: 16) following cycle sequencing are shown. In analysis, the measured result  40  will show an overlap of nucleotides from both amplicons (indicated with *s in 40 and with text set forth in italics in the expected target and marker sequences), but if the marker amplicon contains a poly-A sequence of suitable length at the start (at least as long as the expected sample target sequence), the A channel of the nucleotide detector may be turned off to reveal the sample target sequence (with missing As) followed by the coded marker sequence (with missing As) as shown at  41 . If the sample target sequence is missing, thereby proving a negative result for the presence of the genomic target, only the marker sequence  42  will be revealed (it may not be necessary to switch off the A channel if it is clear that there is no nucleotide overlap in the result). 
         [0105]      FIG. 7  illustrates a more complex application of the present invention intended to be used with the so-called MULTIGEN® technology disclosed in U.S. Pat. No. 6,197,510. Briefly, the MULTIGEN® technology is a way of amplifying and detecting two or more genomic targets at the same time by making the amplification primers designed for the different targets to be of different molecular weights so that the resulting amplicons are of different sizes, thereby allowing separation by gel electrophoresis (Ref. 8). The figure shows three different genomic targets  50 ,  51  and  52  represented as Target 1, Target 2 and Target 3, and three marker sequences  53 ,  54  and  55  (the regions of the markers that will be revealed by cycle sequences), one of which includes a sequence  56  corresponding to Target 1, another 57 corresponding to Target 2 and a third  58  corresponding to Target 3. The markers themselves will contain annealing sites for the PCR primers used for the corresponding genomic targets, and sites for the corresponding sequencing primers. The concept is that, if amplification and sequencing reveals an amplicon containing Target 1, for example, then the conditions for amplification and sequencing of genomic Target 1 are operational, and the absence of a corresponding genomic sequence containing Target 1 will confirm that the genomic target is not present. 
         [0106]    Each of the three marker constructs contains (in the 5′ to 3′ direction) at least one poly-A region  60  on one or both sides of the target sequence, and a final coding sequence  61 . However, the poly-A regions of the three constructs are of such a size and position that, in the output of the electropherogram: 
         [0107]    a. only poly-A regions overlap the sequences from the genomic targets (which themselves do not overlap, as represented at the top of  FIG. 7 , because of the use of sequencing primers of different lengths); 
         [0108]    b. the sequences  56 ,  57  and  58  for Target 1, Target 2 and Target 3 derived from the three markers do not overlap; 
         [0109]    c. the coding sequence  61  from each marker is identically aligned in the output and hence produce a clearly readable result (because the coding region for each marker will be the same). 
         [0110]    Consequently, by turning off the A channel of the electropherogram, all of the sequences of interest (if present in the sample) will be unambiguously aligned in the electropherogram (minus As), thus: Target 1 (genome), Target 2 (genome), Target 3 (genome), Target 1 (marker 1), Target 2 (marker 2), Target 3 (marker 3), coding sequence (marker—providing information). 
         [0111]    The poly-A regions on each side of the target region of the three markers are adjusted to produce these results (with the marker 55 having no poly-A region on the downstream side of the Target 3 region  58 }. It will be seen that the sequenced parts of the three markers are not aligned at the left hand side of the figure, and that the third marker is indented to the right more than the second marker, and the second marker is indented to the right more than the first marker. This represents the different positions at which the read-outs of these parts will commence in the electropherogram due to the use of sequencing primers of different (progressively larger) molecular weight for the three targets 1, 2 and 3 designed to prevent overlap of the read-outs of the target sequences themselves. 
         [0112]    Testing of this kind may be carried out while simultaneously carrying out human (or other) genotyping by detecting short tandem repeats (STRs). This can be done by designing amplification primers for the STR regions of the sample and then separating the resulting amplicons from the others by gel electrophoresis. By using primers of greater length than those used for the genomic targets and the markers, the resulting amplicons for STR will be spaced from the other amplicons during electrophoresis (as represented by their position  70  to the right hand side of  FIG. 7 ). The primers used for the STR amplification are labeled (one primer of each pair) with a fluorescent (or other) tag, whereas the other amplification primers are not, and U is used in place of T in the construction of the STR primers alone. Therefore the STR amplicons will be detectable by the electropherogram (by virtue of their fluorescent tag) even though these amplicons are not sequenced, and the results will show up spaced from the results for the genomic targets and the markers. Sequencing of these amplicons is avoided by not including sequencing primer sites into the STR amplicons and removing PCR and STR primers after the amplification step, but before the cycle sequencing step. There are two main ways in which the PCR and STR primers may be removed, i.e.: 
         [0113]    a. Physical methods e.g. membrane filtration (for example, using the equipment of Millipore, USA); 
         [0114]    b. Chemical methods e.g. the use of Amplirase (Urasil—N-Glycolysase, Applied Biosystems USA). When a PCR reaction mixture is digested with Amplirase, the enzyme digests into bits and pieces (at the base ‘U’) all primers that are not incorporated as well as the primers that are incorporated into the amplicons. The labeled primer for the STR is made in such a way that the first nucleotide other than U from the 3′-end is labeled with a fluorescence marker. There is no U between the labeled nucleotide and the 3′-end of the STR primer. Hence the labeled nucleotide incorporated into the STR amplicon is not removed. 
         [0115]    After the clean up, the reaction mixture will contain unlabeled target amplicons and artificial marker amplicons and labeled STR amplicons only. When proceeding with regular cycle sequencing, the STR amplicons formed will not have any binding sites for those primers used in the cycle sequencing step, but will carry the fluorescence labels. Therefore the STR amplicons will light up and the molecular weights of STR primers are such that the amplicons signals will show outside all the signals produced from cycle sequencing and will not be involved in any sequence analysis. 
         [0116]      FIG. 8  is a diagram similar to  FIG. 7 , but showing the three constructs designed in a different way to achieve the same result. In this case, the coding regions (identical in all three cases) are positioned centrally of the constructs and precisely aligned with each other, with the Target 1, 2 and 3 sequences staggered at the 3′-ends to avoid overlap. The poly-A regions of the three constructs are adjusted in length to achieve this result and to compensate for the differences in length of the sequencing primers used for the genomic targets. Again, STR may be carried out simultaneously in the same way as before, and the resulting electropherogram (when the A channel is turned off) avoids overlap of the sequences of interest, even if all such sequences are present. 
         [0117]    In some embodiments, the methods of this invention include a method of testing for the presence of a target nucleic acid in a sample, which method comprises providing amplification primers designed to anneal to said target nucleic acid flanking a characteristic sequence thereof, carrying out a nucleic acid amplification procedure employing said primers to produce an amplicon containing said characteristic sequence, providing a sequencing primer designed to anneal to said amplicon at a position effective for sequencing said characteristic sequence of said amplicon, and sequencing at least part of said characteristic sequence to confirm the presence said target nucleic acid in said sample, wherein a marker is amplified and sequenced as a control at the same time under identical conditions using identical amplification and sequencing primers, the marker having a unique nucleotide sequence flanked by annealing sites for said amplification and sequencing primers, wherein said target nucleic acid includes a plurality of different characteristic sequences, and amplification and sequencing primers are provided for each one of said plurality of different characteristic sequences, and wherein an equal number of markers as said plurality of different characteristic sequences is provided, each of said markers having a different unique sequence including at least a part identical to one of said characteristic sequences, the part that is identical to one of said characteristic sequences being different in each marker. 
         [0118]    The following Example is provided to further illustrate the present invention. 
       EXAMPLE 
     Sample Preparation 
       [0119]    100 μl of the cell lysate containing RNA virus (Human immune deficiency virus-HIV) and 500 cells of  E. coli  containing a plasmid construct (with codes according to the present invention) is extracted using the RNeasy® Mini Kit, Qiagen, USA). The reagents of the kit are prepared according to the manufacturer&#39;s instructions and 350 μl of RLT buffer and 250 of 100% ethanol are added to 100 μl of viral lysate. The sample is transferred to a spin column and centrifuged at 8,000 rcf for 30 seconds. The sample is washed on the spin column three times, once with 700 μl RW1 buffer and twice with 500 μl RPE buffer. After each wash the spin column is centrifuged at 8000 ref for 30 seconds. After washing, the column is thoroughly dried with a 1-minute centrifugation 8,000 rcf. Finally, the sample is eluted from the column by adding 50 μl RNase-free water to the column and centrifuging for 1 minute at 8,000 rcf. The RNA is further concentrated by re-applying the eluate to the column and centrifuging a second time at 8,000 ref for 1 minute. RNA/NUCLEIC ACIDS concentration is determined using a spectrophotometer (Ultrospec™ 3000 UV Visible Spectrophotometer, Pharmacia Biotech, Cambridge, England). 
       RT-PCR or PCR 
       [0120]    SUPERSCRIPT® One-Step RT-PCR with PLATINUM® Taq kit (Invitrogen, USA) is used for individual RT-PCR. The reaction volume is 50μλ, which consists of 25μλ 2× Reaction mix, 200 nM of each primer, 1 μl RT/Platinum mix Taq and 10 μl of RNA extract. The tubes are placed in a thermocycler, GENEAMP® 2400 PCR System (Applied Biosystems, USA) and amplified according to the following thermocycling profile: 95° C./3 min (95° C./1 min, 55° C./1 min, 72° C./1 min)×35 cycles, &amp; 70° C./10 min. 
         [0121]    The PCR mixture was cleaned up using a PSI Clone™ device (Princeton Separation, NJ, USA) according to the manufacturer&#39;s instructions. 
       Cycle Sequencing 
       [0122]    Amplicons are sequenced by cycle sequencing using ABI PRISM® BIGDYE TERMINATOR Cycle Sequencing Ready Reaction Kit (Applied Biosystems, USA) on a GENEAMP® 2400 thermocycler (PE Applied Biosystems, USA) using thermocycler profile indicated above. Unincorporated dye terminators are removed using CENTRISEP chromatography columns (Princeton, USA). The samples are then dried, and re-suspended in 20 μl of ABI PRISM® Template Suppression Reagent. Samples are analyzed by capillary electrophoresis using the ABI PRISM® Genetic Analyzer  310 . The 47 cm×5OS μm uncoated capillary is filled with a POP-6® polymer (acrylamide/urea polymer) and heated to 50° C. 20 μl of the sequencing mixture are pipetted into a 0.2 mL microfuge tube provided by the manufacturer (Applied Biosystems, USA). Samples are drawn into the capillary by electrokinetic injection at 2 Kv for 50 to 200 seconds. The electrophoresis is carried out at 15 Kv for 20 minutes. 
         [0123]    The sequence is then read using an electropherogram in accordance with the procedure outline above. 
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