序列同源性分析软件Blast的WEB界面构建及其应用

基于局域网(Intranet)内的PC/Linux服务器, 构建了序列同源性分析软件Blast的WEB界面. 局域网内的所有计算机均可通过WEB方式访问该服务器进行公共数据库和自建数据库的查询,具有保密、高效、免费的优点,能够满足实验室和研究院所的大规模、快速数据分析任务.     

Fluorescence energy transfer monitored competitive equilibria of nucleic acids: applications in thermodynamics and screening

Precise thermodynamic characterization of nucleic acid complex stability is required to understand a variety of biologically significant events as well as to exploit the specific recognition capabilities of nucleic acids in biotechnology, diagnostics, and therapeutics. The development of a database of nucleic acid thermodynamics with sufficient precision to foster further developments in these areas requires new and improved measurement techniques. The combination of a competitive equilibrium titration with fluorescence energy transfer based detection provides a method for precise measurement of differences in free energy values for nucleic acid duplexes that far exceeds in precision those accessible via conventional methods. The method can be applied to detect and to characterize any deviation in a nucleic acid that alters duplex stability. Such deviations include, but are not limited to, mismatches; single nucleotide polymorphisms (SNP); chemically modified nucleotide bases, sugars or phosphates; and conformational anomalies or folding motifs, such as, loops or hairpins.     

Sequence errors described in GenBank: a means to determine the accuracy of DNA sequence interpretation.

The accuracy of nucleic acid sequence data interpretation was determined by assessing and quantifying the discrepancies reported in the GenBank database. This permitted the calculation of an Error Rate (ER) for nucleic acid sequence determination. If one assumes that most entries (TB, Total Bases) were independently verified or those without reported discrepancies were correct, the ER is 0.368 errors per 1000 bases. However, if one assumes that only those sequences with reported discrepancies (TBIQ, Total Bases from entries In Question) were verified and are thus correct, the ER is 2.887 errors per 1000 bases. This establishes the first set of limit boundaries of the ER for sequence interpretation and sequence errors within the GenBank database and provides the foundation for future assessments and the monitoring of sequence data accumulation. In addition, the ER measure provides a basis to evaluate the efficiency and merit of present and future automated nucleic acid sequencing technologies which will have a direct impact upon the final outcome of the "Human Genome Initiative".     

'Cyclicons' as hybridization-based fluorescent primer-probes: synthesis, properties and application in real-time PCR

We have studied the use of 'pseudocyclic oligonucleotides' (PCOs) (Jiang et al. Bioorg. Med. Chem. 1999, 7, 2727) as hybridization-based fluorescent probes. The resulting fluorescent tag-attached PCOs are called 'cyclicons'. Cyclicons consist of two oligonucleotides linked to each other through 3'-3' or 5'-5' ends. One of the oligos is the probe or primer-probe sequence that is complementary to a target nucleic acid (mRNA/DNA), and the other is a modifier oligo that is complementary to one of the ends of the probe oligo. A fluorescence molecule and a quencher molecule are attached at an appropriate position in the cyclicons. In the absence of the target nucleic acid, the fluorophore and the quencher are brought in close proximity to each other because of the formation of an intramolecular cyclic structure, resulting in fluorescence quenching. When the cyclicon hybridizes to the complementary target nucleic acid strand, the intramolecular cyclic structure of the cyclicon is destabilized and opened up, separating the fluorophore and quencher groups, resulting in spontaneous fluorescence emission. Fluorescent studies in the presence and absence of a target nucleic acid suggest that cyclicons exist in intramolecular cyclic structure form in the absence of the target and form the duplex with the target sequence when present. Both the cyclicons are useful for nucleic acid detection. The studies with DNA polymerase on 5'-5'-attached cyclicons suggest that the presence of quencher moiety in the probe sequence does not inhibit chain elongation by polymerase. The experiments with a 5'-5'-attached cyclicon suggest the new design serves as an efficient unimolecular primer-probe in real-time PCR experiments.     

Characterization of the distribution of potential short restriction fragments in nucleic acid sequence databases: Implications for an alternative to chemical synthesis of oligonucleotides

We have searched the GenBank nucleic acid sequence database for potential short restriction fragments. All possible oligonucleotides up to length five are found at least once flanked by known restriction recognition patterns. Thus, searches in the database for a specific sequence corresponding to a desired oligonucleotide would often point to one or more sources of short, retrievable fragments containing that sequence. These results underscore the potential of nucleic acid sequence databases in planning experiments.     

CABIOS REVIEW: The GenBank nucleic acid sequence database

‘The GenBank’^* nucleic acid sequence database isa computer-based collection of all published DNA and RNA sequences;it contains over five million bases in close to six thousandsequence entries drawn from four thousand five hundred publishedarticles. Each sequence is accompanied by relevant biologicalannotation. The database is available either on magnetic tape,on floppy diskettes, on-line or in hardcopy form. We discussthe structure of the database, the extent of the data and theimplications of the database for research on nucleic acids.     

Fluorescence energy transfer monitored competitive equilibria of nucleic acids: Applications in thermodynamics and screening

Precise thermodynamic characterization of nucleic acid complex stability is required to understand a variety of biologically significant events as well as to exploit the specific recognition capabilities of nucleic acids in biotechnology, diagnostics, and therapeutics. The development of a database of nucleic acid thermodynamics with sufficient precision to foster further developments in these areas requires new and improved measurement techniques. The combination of a competitive equilibrium titration with fluorescence energy transfer based detection provides a method for precise measurement of differences in free energy values for nucleic acid duplexes that far exceeds in precision those accessible via conventional methods. The method can be applied to detect and to characterize any deviation in a nucleic acid that alters duplex stability. Such deviations include, but are not limited to, mismatches; single nucleotide polymorphisms (SNP); chemically modified nucleotide bases, sugars or phosphates; and conformational anomalies or folding motifs, such as, loops or hairpins. © 2002 Wiley Periodicals, Inc. Biopoly (Nucleic Acid Sci) 61: 214–223, 2002     

Database of mutations that alter the large tumor antigen in simian virus 40.

The SV40 T antigen database is a listing of plasmids and/or viruses that express mutant forms of the virus-encoded large T antigen protein. The parental virus strain, nucleic acid sequence of the mutations, the effect of the mutation on the T antigen amino acid sequence, and key references are included in the listing. The database is available from the authors as a Macintosh FileMaker Pro file, and as a hard copy printout.     

Allosteric aptamers: targeted reversibly attenuated probes

Aptamers are unique nucleic acids with regulatory potentials that differ markedly from those of proteins. A significant feature of aptamers not possessed by proteins is their ability to participate in at least two different types of three-dimensional structure: a single-stranded folded structure that makes multiple contacts with the aptamer target and a double-helical structure with a complementary nucleic acid sequence. We have made use of this structural flexibility to develop an aptamer-based biosensor (a targeted reversibly attenuated probe, TRAP) in which hybridization of a cis-complementary regulatory nucleic acid (attenuator) controls the ability of the aptamer to bind to its target molecule. The central portion of the TRAP, between the aptamer and the attenuator, is complementary to a target nucleic acid, such as an mRNA, which is referred to as a regulatory nucleic acid (regNA) because it regulates the activity of the aptamer in the TRAP by hybridization with the central (intervening) sequence. The studies reported here of the ATP-DNA TRAP suggest that, as well as inhibiting the aptamer, the attenuator also acts as a structural guide, much like a chaperone, to promote proper folding of the TRAP such that it can be fully activated by the regDNA. We also show that activation of the aptamer in the TRAP by the complementary nucleic acid at physiological temperatures is sensitive to single-base mismatches. Aptamers that can be regulated by a specific nucleic sequence such as in an mRNA have potential for many in vivo applications including regulating a particular enzyme or signal transduction pathway or imaging gene expression in vivo.     

Light-up probes: thiazole orange-conjugated peptide nucleic acid for detection of target nucleic acid in homogeneous solution

We have constructed light-up probes for nucleic acid detection. The light-up probe is a peptide nucleic acid (PNA) oligonucleotide to which the asymmetric cyanine dye thiazole orange (TO) is tethered. It combines the excellent hybridization properties of PNA and the large fluorescence enhancement of TO upon binding to DNA. When the PNA hybridizes to target DNA, the dye binds and becomes fluorescent. Free probes have low fluorescence, which may increase almost 50-fold upon hybridization to complementary nucleic acid. This makes the light-up probes particularly suitable for homogeneous hybridization assays, where separation of the bound and free probe is not necessary. We find that the fluorescence enhancement upon hybridization varies among different probes, which is mainly due to variations in free probe fluorescence. For eight probes studied the fluorescence quantum yield at 25 degrees C in the unbound state ranged from 0.0015 to 0.08 and seemed to depend mainly on the PNA sequence. The binding of the light-up probes to target DNA is highly sequence specific and a single mismatch in a 10-mer target sequence was readily identified.     

A high throughput method to investigate oligodeoxyribonucleotide hybridization kinetics and thermodynamics.

We describe a high throughput microtiter-based assay to measure binding of oligodeoxyribonucleotides to nucleic acid targets. The assay utilizes oligodeoxyribonucleotide probes labeled with a highly chemiluminescent acridinium ester (AE). Reaction of AE with sodium sulfite renders it non-chemiluminescent. When an AE-labeled probe hybridizes to a target nucleic acid AE is protected from reaction with sodium sulfite and thus remains chemiluminescent. In contrast, unhybridized probe readily reacts with sodium sulfite and is rendered non-chemiluminescent. Hybridization of an AE-labeled probe to a target nucleic acid can therefore be detected without physical separation of unhybridized probe by treatment of the hybridization reaction with sodium sulfite and measurement of the remaining chemiluminescence. Using this method we measured hybridization rate constants and thermodynamic affinities of oligodeoxyribonucleotide probes binding to simple synthetic targets as well as large complex biological targets. The kinetic and thermodynamic parameters were measured with a high degree of accuracy and were in excellent agreement with values measured by other established techniques.     

Smart probe: a novel fluorescence quenching-based oligonucleotide probe carrying a fluorophore and an intercalator.

A novel probe (Smart probe) has been developed for nucleic acid detection. The smart probe is an oligodeoxyribonucleotide carrying a fluorophore and an intercalator internally. Fluorescence of the smart probe is quenched by the intercalator in the absence of target sequence. While upon hybridization the probe emits greater fluorescence due to the interference of quenching by intercalation. The smart probe has been shown to recognize a single base mismatch in the double-stranded form without utilizing thermal stability difference of hybrids.     

A single-stranded nucleic acid binding sequence common to the heterogeneous nuclear ribonucleoparticle protein A1 and murine recombinant virus gp70.

We have used an antisynthetic peptide antiserum to a murine recombinant virus gp70 to probe normal mouse tissues for immunologically related proteins. In addition to cognate gp70s, this antiserum reacts with the heterogeneous nuclear ribonucleoparticle protein A1 by virtue of a 5-amino acid epitope, PRNQG. Further structural similarity is evident both 5' and 3' of this epitope. Since the function of the heterogeneous nuclear ribonucleoprotein particles in the cell is to aid in the stabilization and processing of newly synthesized RNA, we have investigated whether this retroviral sequence exhibits any nucleic acid-binding properties by the same criteria established for the identification of heterogeneous nuclear ribonucleoprotein particles. Analysis of the peptide in a poly(eA) binding assay shows this retroviral sequence to bind with high affinity to single-stranded nucleic acid. This binding occurs in a salt-sensitive manner characteristic of single-stranded nucleic acid-binding proteins. Flanking peptides not containing this sequence generated from either the A1 or gp70 show no ability to bind single-stranded nucleic acids by this assay.     

General methods of sequence comparison

Mathematical methods for comparison of nucleic acid sequences are reviewed. There are two major methods of sequence comparison: dynamic programming and a method referred to here as the regions method. The problem types discussed are comparison of two sequences, location of long matching segments, efficient database searches and comparison of several sequences. This work was supported by a grant from the System Development Foundation.     

Nucleic acid structure and sequence probing using fluorescent base analogue tC(O)

The fluorescent cytosine analog tC(O) is on average the brightest probe of its kind and, moreover, it introduces minimal perturbations to the normal secondary structure of DNA. Here several ways of how tC(O), with an advantage, can be used as a local fluorescent probe in nucleic acid systems are presented. Most importantly, we show that tC(O) is an excellent probe for the detection of individual melting processes of complex nucleic acid structures containing a large number of separate secondary structure motifs. Since conventional UV-melting investigations merely monitor the global melting process of the whole nucleic acid structure, e.g. multi-hairpin systems in RNA/DNA, and thus is incapable of estimating individual melting transitions of such systems, tC(O) represents a new method of characterization. Furthermore, we find that tC(O) may be used to detect bulges and loops in nucleic acids as well as to distinguish a matched base-pair from several of the mismatched.     

Nucleic acid hybridization assays employing dA-tailed capture probes. I. Multiple capture methods

A quantitative hybridization assay termed "reversible target capture" is described. The technique is designed to extensively purify the target nucleic acid from crude cell lysates in about 1 h without phenol extraction. Simple, rapid methods are described that explain how each process in the assay is optimized. The procedure involves hybridizing the target nucleic acid in solution with a dA-tailed capture probe and a labeled probe. The capture probe-target-labeled probe "ternary complex" is then captured on magnetic beads containing oligo(dT). After the excess unhybridized labeled probe, cell debris, and other sample impurities are washed away, the intact ternary complex is further purified by chemical elution from the beads and recapture on fresh beads. The ternary complex is then eluted thermally and recaptured on a third set of beads or on poly(dT) filters. This triple capture method results in a detection limit of approximately 0.2 amol (100 fg) of target with 32P-labeled riboprobes. This is approximately 1000 times more sensitive than sandwich assays employing only a single capture step. The method is illustrated by detecting Listeria cells in the presence of heterologous bacteria. With three rounds of target capture, as few as six Listeria cells have been detected in the presence of 1.25 x 10(7) control cells.     

Development of Internal Controls for Probe-Based Nucleic Acid Diagnostic Assays

A method is described for the design, evaluation, and application of internal control targets and probes for use in probe-based nucleic acid diagnostic assays (i.e., PCR-ELISA). The technique is a modified version of oligonucleotide-directed mutagenesis in conjunction with PCR amplification to develop a novel probe-annealing sequence in a cloned IS1111a gene fragment of Coxiella burnetii. The internal control probe-recognition site with its complementary probe was identical to the wild-type-specific probe in length, base composition, location, and annealing temperature. Neither the internal control nor the wild-type probes annealed to the recognition sequence of the other. As both of the amplified nucleic acid fragments, internal control and wild type, were identical in length and base composition, the amplification conditions for the diagnostic assay were not affected. This allowed small copy numbers of the internal control clone to be loaded into a diagnostic assay without negatively affecting it. In a single reaction we were able to differentiate between an assay reporting a true or false-negative signal. A negative signal is defined as the absence of detectable pathogen genetic material (true) or inhibition/failure of the reaction (false).     

Identification of novel restriction endonuclease-like fold families among hypothetical proteins

Restriction endonucleases and other nucleic acid cleaving enzymes form a large and extremely diverse superfamily that display little sequence similarity despite retaining a common core fold responsible for cleavage. The lack of significant sequence similarity between protein families makes homology inference a challenging task and hinders new family identification with traditional sequence-based approaches. Using the consensus fold recognition method Meta-BASIC that combines sequence profiles with predicted protein secondary structure, we identify nine new restriction endonuclease-like fold families among previously uncharacterized proteins and predict these proteins to cleave nucleic acid substrates. Application of transitive searches combined with gene neighborhood analysis allow us to confidently link these unknown families to a number of known restriction endonuclease-like structures and thus assign folds to the uncharacterized proteins. Finally, our method identifies a novel restriction endonuclease-like domain in the C-terminus of RecC that is not detected with structure-based searches of the existing PDB database.