Medical utilisation and costs in panic disorder: a comparison with social phobia

There is considerable evidence that people with panic disorder utilise the physical health care system more frequently than people in the general community and so incur for themselves, and impose on the public health care system, considerably greater costs. Although this is probably because of specific characteristics to do with panic disorder, it may also be a function of having any anxiety disorder where panic is prominent. This study represents one of the few comparisons of medical utilisation and costs incurred by people with panic disorder to those incurred by people with another anxiety disorder, in this case, social phobia. Before treatment, 41 people with panic disorder, 15 with social phobia and 43 nonanxious controls were interviewed about their use of the medical care system over the previous 12 months. As expected, people with panic disorder had significantly higher utilisation rates than either the nonanxious controls or the socially phobic subjects, and incurred substantially higher costs. Adequate screening for panic disorder at the primary medical care level together with appropriate treatment referral therefore have the potential to substantially reduce the personal and community costs incurred by people with panic disorder.

Avian IFN-gamma genes: sequence analysis suggests probable cross-species reactivity among galliforms

Little is known about the evolution of cytokines in non-mammalian systems. To address this problem, we attempted to clone the gene for interferon-gamma (IFN-gamma) from a variety of avian species using oligonucleotide primers based on the sequence of the chicken IFN-gamma gene. The coding sequence and partial intron sequences were determined for four species, namely guinea fowl, ring-necked pheasant, Japanese quail, and turkey. To obtain sequence information on the gene extremities, a modified 5' and 3' RACE protocol was used. The sequence information showed that the coding regions of the IFN-gamma gene are highly conserved among the species studied (93.5%-96.7% and 87.8%-97.6% at the nucleotide and peptide levels, respectively) and are more conserved at the amino-terminal region (exons 1 and 2) than the carboxyl-terminal (exons 3 and 4). This high degree of overall identity at the predicted primary amino acid sequence level of the protein, including the deduced IFN-gamma receptor binding motifs, suggests that IFN-gamma may be cross-reactive among these species. Phylogenetic analysis shows that the similarity of the avian IFN-gamma sequences parallels the presumed evolutionary relationships between the species.

Fiber-coupled high-power external-cavity semiconductor lasers for real-time Raman sensing

High-power, external-cavity semiconductor lasers with narrow bandwidth and fiber-coupled output are designed and constructed. An output power of 540 mW is coupled out of a 100-mum multimode fiber with coupling efficiency of 72% when the laser is operated at 1.1 A. The emission linewidth is as narrow as 22 GHz, and the wavelength is tunable from 779.7 to 793.0 nm. Application of such lasers to remote real-time Raman sensing of materials is also demonstrated.

A surface-based approach to DNA computation

A scalable approach to DNA-based computations is described. Complex combinatorial mixtures of DNA molecules encoding all possible answers to a computational problem are synthesized and attached to the surface of a solid support. This set of molecules is queried in successive MARK (hybridization) and DESTROY (enzymatic digestion) operations. Determination of the sequence of the DNA molecules remaining on the surface after completion of these operations yields the answer to the computational problem. Experimental demonstrations of aspects of the strategy are presented.

DNA computing on surfaces: encoding information at the single base level

The feasibility of encoding a bit (0 or 1) of information for DNA-based computations at the single nucleotide level is evaluated, particularly with regard to the efficiency and specificity of hybridization discrimination. Hybridization experiments are performed on addressed arrays of 32 (2(5)) distinct oligonucleotides immobilized on chemically modified glass and gold surfaces with information encoded in a binary (base 2) format. Similar results are obtained on both glass and gold surfaces and the results are generally consistent with thermodynamic calculations of matched and mismatched duplex stabilities. It is found that under the conditions required to obtain single nucleotide specificity in the hybridization process, hybridization efficiency is low, compromising the utility of single nucleotide encoding for DNA computing applications in the absence of some additional mechanism for increasing specificity. Several methods are suggested to provide such increased discrimination.

An approach to predicting the stabilities of peptide nucleic acid:DNA duplexes

An approach is described for predicting peptide nucleic acid (PNA):DNA duplex stability from base sequence by approximating the total free energy of dissociation, delta G degree tot, for these duplexes as the sum of five parameters: (a) a nearest-neighbor interaction summation term, sigma Nj delta G degree j; (b) an initiation term, delta G degree i; (c) a dangling-end stabilization term, delta G degree e; (d) a PNA:DNA stabilization term per nearest-neighbor interaction, delta G degree pna; and (e) an ionic strength term, delta G degree Na. Parameters (a) and (b) are approximated using previously determined values for DNA:DNA duplexes, whereas parameters (c), (d), and (e) are empirically determined. These terms are used to calculated delta G degree tot, which is used in conjunction with a transition enthalpy (delta H degree) value, also approximated from nearest-neighbor values previously derived for DNA:DNA duplexes, to calculate a melting temperature (Tm) for the PNA:DNA duplex. Predicted Tm values calculated by this approach agreed fairly well with measured values for 11 different PNA:DNA duplexes, as well as with literature values. The approach also accurately models ionic strength effects.

A software system for data analysis in automated DNA sequencing

Software for gel image analysis and base-calling in fluorescence-based sequencing consisting of two primary programs, BaseFinder and GelImager, is described. BaseFinder is a framework for trace processing, analysis, and base-calling. BaseFinder is highly extensible, allowing the addition of trace analysis and processing modules without recompilation. Powerful scripting capabilities combined with modularity and multilane handling allow the user to customize BaseFinder to virtually any type of trace processing. We have developed an extensive set of data processing and analysis modules for use with the program in fluorescence-based sequencing. GelImager is a framework for gel image manipulation. It can be used for gel visualization, lane retracking, and as a front end to the Washington University Getlanes program. The programs were designed using a cross-platform development environment, currently allowing them to run in Windows NT, Windows 95, Openstep/Mach, and Rhapsody. Work is ongoing to deploy the software on additional platforms, including Solaris, Linux, and MacOS. This software has been thoroughly tested and debugged in the analysis of >2 million bp of raw sequence data from human chromosome 19 region q13. Overall sequencing accuracy was measured using a significant subset of these data, consisting of approximately 600 sequences, by comparing the individual shotgun sequences against the final assembled contigs. Also, results are reported from experiments that analyzed the accuracy of the software and two other well-known base-calling programs for sequencing the M13mp18 vector sequence. [The sequence data described in this paper have been submitted to the GenBank data library under accession no. AF025422]

Peripheral primitive neuroectodermal tumor presenting with diffuse cutaneous involvement and 7;22 translocation

We report an unusual case of peripheral primitive neuroectodermal tumor (pPNET) in an infant presenting with congenital cutaneous nodules and a t(7;22)(p21;q11.2). The biologic behavior of the tumor diverged over time from a slowly growing tumor with multiple cutaneous nodules to a more aggressive neoplasm characterized by pulmonary metastases and a soft tissue mass showing additional cytogenetic alterations.

MALDI-TOF mass spectrometric typing of single nucleotide polymorphisms with mass-tagged ddNTPs

A matrix-assisted laser desorption/ionization time-of-flight mass spectrometry based method has recently been reported for the typing of single nucleotide polymorphisms using single nucleotide primer extension. This method is limited in some cases by the resolution of the mass determination, as the mass difference between nucleotides can be as little as 9 Da (the difference between A and T). A variation of this method is described here in which a mass-tagged dideoxynucleotide is employed in the primer extension reactions in place of the unmodified dideoxynucleotide. The increased mass difference due to the presence of the mass-tags substantially improves the accuracy and versatility of the procedure.

Antigenic variants of J subgroup avian leukosis virus: sequence analysis reveals multiple changes in the env gene

HPRS-103, the prototype of avian leukosis virus (ALV) subgroup J, was isolated in 1989 from meat-type chickens from commercial flocks where it induces myelocytic myeloid leukosis (ML). The HPRS-103 env gene differs considerably from other ALV subgroups but shows high identity (75-97%) to env-like sequences of the different members of the EAV family of endogenous avian retroviruses. Recently, we have isolated several viruses related to HPRS-103 from cases of ML. Although these isolates showed properties of ALV subgroup J, the majority of them resisted neutralization by HPRS-103-specific serum, suggesting antigenic variation. The nucleotide sequence of the env gene of the variant viruses showed several substitutions resulting in amino acid changes especially clustered in the variable regions hr1, hr2 and vr3. Analysis of the data suggests that selection pressure, probably from the immune response, is driving the antigenic variation among the isolates. Phylogenetic analysis of the sequences showed the evolutionary relationships of the isolates with HPRS-103 and the EAV family of endogenous avian retroviruses. The epidemiological significance of the antigenic variation and the emergence of variant viruses are discussed.

Development and application of polymerase chain reaction (PCR) tests for the detection of subgroup J avian leukosis virus

Subgroup J avian leukosis virus (ALV) is a recently identified avian retrovirus associated with myeloid leukosis in meat-type chickens. The env gene of the HPRS-103 strain of ALV, the prototype of this subgroup, differs considerably from that of other subgroups, but shows close homology to the env-like sequences of members of the EAV family of endogenous retroviruses. Polymerase chain reaction (PCR) tests using two sets of primers were developed for the specific detection of the members of this new subgroup along with another pair of primers for detecting other subgroup viruses. The specificity and sensitivity of this detection system was compared with the conventional detection methods in experimentally and naturally infected samples. The use of PCR was found to be rapid, specific and more sensitive than the conventional diagnostic tests for the detection of ALV. Moreover, the two subgroup J ALV-specific PCR tests were found to be capable of differentiating between 'prototype-like' viruses and more recent isolates which show extensive antigenic and sequence variations. The use of this test as a rapid and sensitive method of detection of viruses in epidemiological studies and eradication programs is discussed.

Attachment of group B streptococci to macrophages is mediated by a 21-kDa protein

Group B Streptococcus (GBS) is able to bind to human macrophages in vitro in the absence of exogenous opsonins. The exact mechanisms that mediate this attachment are unclear. This study was undertaken to determine what protein adhesins are present on the surface of GBS that mediate attachment to macrophages. We have identified a 21-kDa protein from the envelope of GBS type III that directly binds to macrophages as determined by Western blot analysis. Antiserum against this protein was able to inhibit binding of GBS to macrophages by greater than 80% as measured by flow cytometry. Antiserum against the 21-kDa protein cross-reacted with 21-kDa proteins from GBS type Ib, type II, type III (COH31 and MR732) and type IV, as well as Staphyloccus epidermidis, but not GBS type Ia, Listeria monocytogenes or Enterococcus faecalis. This protein may be important in mediating the attachment of GBS to macrophages in an opsonin-poor environment.

The immunophilin FKBP65 forms an association with the serine/threonine kinase c-Raf-1

FKBP65 is a member of the FK506-binding protein class of immunophilins and is the only member reported to contain four peptidylprolyl cis-trans isomerase domains and an unrelated COOH-terminal domain. In this report, we show that the heat shock protein hsp90 and the serine/threonine protein kinase c-Raf-1 are components of FKBP65 immune complexes. The NH2-terminal regulatory domain of c-Raf-1 appears to be required for its interaction with FKBP65. Using GST-FKBP65 fusion protein and purified Raf proteins, we show that full-length FKBP65 can interact with c-Raf-1 but not B-Raf. The activation kinetics of c-Raf-1 after v-H-RasV12 injection of Xenopus oocytes appear to correlate with FKBP65/c-Raf-1 interaction, suggesting that FKBP65 may preferentially associate with forms of c-Raf-1 that are more posttranslationally modified. The interaction of FKBP65 with the c-Raf-heat shock protein 90 heterocomplex implicates this immunophilin in signal-transduction processes.

Genetic analysis by peptide nucleic acid affinity MALDI-TOF mass spectrometry

The ability to analyze multiple polymorphic sites rapidly and accurately is crucial in all areas of genetic analysis. We have developed an approach for the detection of multiple point mutations, using allele-specific, mass-labeled, peptide nucleic acid (PNA) hybridization probes, and direct analysis by matrix-assisted laser desorption/ionization time-of-flight mass spectrometry. The composite mass spectra produced contain peaks of distinct masses corresponding to each allele present, resulting in a mass spectral "fingerprint" for each DNA sample. The hybridization characteristics of PNA:DNA duplexes were found to be highly dependent on both base content and sequence. Results from the analysis of four polymorphic sites contained in exon 4 of the human tyrosinase gene show that this approach is simple, rapid, and accurate with potential applications in many areas of genetic analysis.

Demonstration of a word design strategy for DNA computing on surfaces

A strategy for DNA computing on surfaces using linked sets of 'DNA words' that are short oligonucleotides (16mers) is proposed. The 16mer words have the format 5'-FFFFvvvvvvvvFFFF-3' in which 4-8 bits of data are stored in 8 variable ('v') base locations, and the remaining fixed ('F') base locations are used as a word label. Using a template and map strategy, a set of 108 8mers each of which possesses at least a 4 base mismatch with the complements to all the other members of the set (4bm complements) are identified for use as a variable base sequence set. In addition, sets of 4 and 12 word labels of the form ABCD....DCBA that are respectively 8bm and 6bm complements with each other are identified. The 16mers are chosen to have a G/C content of 50% in order to make the thermodynamic stability of the perfectly matched hybridized DNA duplexes similar; a simple pairwise additive method is used to estimate the perfect match and mismatch hybridization thermodynamics. A series of preliminary experiments are presented that use small arrays of 16mers attached to chemically modified gold surfaces and fluorescently labeled complements to study the hybridization adsorption and enzymatic manipulation of the oligonucleotides.

2'-Fluoro modified nucleic acids: polymerase-directed synthesis, properties and stability to analysis by matrix-assisted laser desorption/ionization mass spectrometry

Fragmentation is a major factor limiting mass range and resolution in the analysis of DNA by matrix-assisted laser desorption/ionization mass spectrometry (MALDI-MS). Protonation of the nucleobase leads to base loss and backbone cleavage by a mechanism similar to the depurination reactions employed in the chemical degradation method of DNA sequencing. In a previous study [Tang,W., Zhu,L. and Smith,L.M. (1997) Anal. Chem ., 69, 302-312], the stabilizing effect of substituting the 24 hydrogen with an electronegative group such as hydroxyl or fluorine was investigated. These 24 substitutions stabilized the N-glycosidic linkage, blocking base loss and subsequent backbone cleavage. For such chemical modifications to be of practical significance, it would be useful to be able to employ the corresponding 24-modified nucleoside triphosphates in the polymerase-directed synthesis of DNA. This would provide an avenue to the preparation of 24-modified PCR fragments and dideoxy sequencing ladders stabilized for MALDI analysis. In this paper methods are described for the polymerase-directed synthesis of 24-fluoro modified DNA, using commercially available 24-fluoronucleoside triphosphates. The ability of a number of DNA and RNA polymerases to incorporate the 24-fluoro analogs was tested. Four thermostable DNA polymerases [Pfu (exo-), Vent (exo-), Deep Vent (exo-) and UlTma] were found that were able to incorporate 24-fluoronucleotides with reasonable efficiency. In order to perform Sanger sequencing reactions, the enzymes' ability to incorporate dideoxy terminators in conjunction with the 24-fluoronucleotides was evaluated. UlTma DNA polymerase was found to be the best of the enzymes tested for this purpose. MALDI analysis of enzymatically produced 24-fluoro modified DNA using the matrix 2,5-dihydroxy benzoic acid showed no base loss or backbone fragmentation, in contrast to the extensive fragmentation evident with unmodified DNA of the same sequence.

Evidence for signaling between the phytopathogenic fungus Pythium ultimum and Pseudomonas fluorescens F113: P. ultimum represses the expression of genes in P. fluorescens F113, resulting in altered ecological fitness

There is increasing evidence that communication between members of the same species, as well as members of different species, is important for the survival of microorganisms in diverse ecological niches, such as the rhizosphere. To investigate whether the phytopathogen Pythium ultimum could alter gene expression in the biocontrol strain Pseudomonas fluorescens F113, which protects the roots of sugar beet from the fungus, a screening system was developed to detect differential expression of bacterial genes in the presence of P. ultimum. The transposon Tn5, containing a promoterless lacZ reporter gene, was used to generate a library of transcriptional gene fusions in P. fluorescens F113. By this screening procedure, five P. fluorescens F113 gene clusters were identified and shown to be repressed in the presence of P. ultimum. The ecological fitness of three of the five reporter mutants in the rhizosphere of seed-inoculated sugar beet was lower than that of the wild type. Furthermore, all five mutants were impaired in their ability to subsequently colonize the rhizosphere of uninoculated sugar beet sown repeatedly in the same soil. With the exception of reporter mutant SF10, which was impaired in nitrogen metabolism, the reporter mutants had growth requirements and biocontrol abilities similar to those of the wild type. This is the first reported case of a fungus repressing the expressing of bacterial genes.

Comparison of traps and development of a two-stage sampling plan for smokybrown cockroaches (Dictyoptera: Blattidae) outdoors

Four commercial sticky traps were compared with jar traps for sampling smokybrown cockroaches, Periplaneta fuliginosa (Serville), outdoors. Lo-Line and Raid Roach Traps caught more cockroaches than jar traps, whereas the Mr. Sticky and Roach Motel caught < 40% of the cockroaches caught in jar traps. Sampling properties of traps (data collected over 4 yr and 3 cities) were examined retrospectively. Taylor's a and b coefficients were both significantly > 1 for jar traps, Raid Roach Trap, and Lo-Line trap. Estimating cockroach catch typical of Alabama (< 3 per trap) at single houses would require > 20 traps with a precision of 0.25 (i.e., standard error as a proportion of the mean). Taylor's power law was also used as a predictor for within-house (i.e., pooled within-house) and between-house catch variances. Coefficients for these predictors are presented that can be used in a fixed-precision 2-stage sampling plan to estimate cockroach catch from large areas.

Evaluation of methods of insecticide application for control of smokybrown cockroaches (Dictyoptera: Blattidae)

The insecticide components of a previously developed integrated pest management system for smokybrown cockroaches, Periplaneta fuliginosa (Serville), were tested individually and at reduced application rates in 4 separate trials over 2 yr. A 2-bait combination (pellet and gel baits) did not significantly reduce cockroach abundance more than a single constituent bait alone. A targeted spray of trelamethrin was significantly less effective than a 2-bait combination. Residual activity of insecticides was determined with American cockroaches, P. americana (L.), in a laboratory bioassay. Chlorpyrifos wettable powder remained active < 12 d in the field, after which time its activity was not different from an experimental control (no insecticide residues), whereas chlorpyrifos pellet and hydramethylnon paste baits retained initial activity for > 27 d. Nematodes [Steinernema carpocapsae (Weiser)] applied as a spray solution did not effect the abundance of smokybrown cockroaches, and no cockroaches were recovered that exhibited nematode infection. Time needed to apply various insecticide treatments did not differ substantially (15-25 min per house), even for lower application rates.

Comparison of different regimens of electrical stimulation applied to nonmobilized and newly mobilized latissimus dorsi muscle

We investigated the possibility of preventing further aggravation of muscle ischemia and necrosis in newly mobilized, unconditioned latissimus dorsi muscle (LDM) by utilizing short increments of stimulation with intervening rest periods. Adult St. Croix sheep (N = 12) weighing 30 +/- 8 kg were used in this study. Fatigue tests (30 min) using different stimulation regimens before and after LDM mobilization were performed on all animals; the length of time to return to baseline levels was also measured. Our investigation yielded results that contradict the conventional wisdom that any electrical stimulation damages newly mobilized LDM and will cause a considerable decrease in contractile force (CF). Stimulation regimens using continuous contractions at 30 and 60 contractions per minute (CPM) for 30 minutes were damaging to the LDM. CF also dropped significantly and returned slowly to baseline values: at 60 CPM, CF dropped to 50 +/- 4% and did not return to baseline even after 90 minutes of rest; at 30 CPM, CF dropped to 61 +/- 4% and baseline was restored after 80 minutes of rest. Electrical stimulation using continuous contractions at a slower rate (15 CPM) was tolerable, although a 23% decrease in CF was noted (p < 0.05 when compared to 60 CPM). These results did not satisfy us that such a regimen would be useful for cardiac assistance immediately after cardiomyoplasty. The work-rest regimen at 30 CPM also gave poor results: CF decreased to 75 +/- 2% and baseline was restored after 80 minutes of rest. Promising results were seen when utilizing a work-rest regimen at 15 CPM. The newly mobilized LDM showed no visible signs of fatigue: CF decreased minimally to 92 +/- 3% (p < 0.05 when compared to 30 CPM), and light microscopic analysis of biopsies revealed no morphological damage exceeding that typically seen after subtotal mobilization. Such results open avenues for future investigations: beginning electrical stimulation immediately after cardiomyoplasty (using a single impulse and a slow rate of contraction); decreasing the length of time necessary to obtain full cardiac assistance; and beginning partial cardiac assistance immediately after cardiomyoplasty (if needed) for approximately 30 minutes several times a day.

Breast cancer cells have lower activating protein 1 transcription factor activity than normal mammary epithelial cells

To determine whether normal breast cells have different levels of activating protein 1 (AP-1) expression and activation relative to breast cancer cells, we have compared the level of c-Jun and c-Fos expression and AP-1 activity in human mammary epithelial cells (HMECs) at different stages of transformation (normal proliferating HMECs, immortal HMECs, oncogene-transformed HMECs, and breast cancer cell lines). These studies demonstrated that normal and immortal HMECs have a high basal level of expression of cJun and cFos and higher AP-1 DNA-binding and transcriptional activating activities than do oncogene-transformed HMECs or human breast cancer cells, with a gradual decrease in AP-1 transactivating activity as cells progress through the carcinogenesis pathway (normal > immortal > oncogene-transformed > cancer cell lines). The AP-1 activity in normal or immortal cells was not modulated by growth factor supplementation or oncogene overexpression, as it is in breast cancer cells. However, the addition of suramin, a nonspecific growth factor antagonist, did inhibit AP-1 in these HMECs, suggesting that this high level of AP-1 present in normal HMECs may be due to autocrine stimulation of growth factor pathways. The differences in AP-1 activity in normal and malignant breast cells may indicate that normal cells are more dependent on AP-1-mediated signals for their growth than are breast cancer cells.

Measurement of NO synthesis in humans by L-[15N2]arginine: application to the response to vaccination

Induction of nitric oxide (NO) synthesis is a key element of the inflammatory response in humans. We describe a sensitive gas isotope ratio mass spectrometric (GIRMS) method for measuring urinary [15N]nitrate production during intravenous infusion of L-[guanidino-15N2]arginine and its application to investigate the effects of a controlled inflammatory stimulus, typhoid vaccination, on NO synthesis in humans. Intravenous infusion of L-[15N2]arginine at 5-12 mumol.kg-1.h-1 for 24 h in three subjects was used to determine arginine and nitrate pool kinetics. Eight subjects received primed constant infusion of 2.5 mumol.kg-1.h-1 of L-[15N2]arginine for 12 h once before and again after typhoid vaccination. NO synthesis was calculated from 15N enrichment of plasma arginine and urinary nitrate, measured by gas chromatography mass spectrometry and GIRMS, respectively, and total urinary nitrate excretion. Baseline NO synthesis was 298 +/- 44 nmol.h-1.kg lean body mass-1, representing 0.41% of arginine flux. After vaccination, NO synthesis (267 +/- 77 nmol.h-1.kg-1) was not increased (P = 0.18), despite demonstration of an acute phase response. Typhoid vaccination is not accompanied by accelerated NO synthesis.

Ligation-mediated PCR amplification of specific fragments from a class-II restriction endonuclease total digest

A method is described which permits the ligation- mediated PCR amplification of specific fragments from a Class-II restriction endonuclease total digest. Feasibility was tested using Bcl I and phage lambda DNA as a model enzyme and amplicon system, respectively. Bcl I is one of many widely used restriction enzymes which cleave at palindromic recognition sequences and leave 5'-protruding ends of defined sequence. Using a single pair of universal primers, a given fragment can be specifically amplified after joining the fragments to adaptors consisting of a duplex primer region and a 9-nucleotide protruding single-stranded 5'-end containing the sequence complementary to the cleaved restriction site and a 4-nucleotide 'indexing sequence.' The protruding strand anneals to a restriction fragment by displacing its corresponding strand in the same fragment-specific indexing sequence located juxtaposed to the restriction site. The adaptor is covalently linked to the restriction fragment by T4 DNA ligase, and amplification is carried out under conditions for long-distance PCR using the M13 forward and reverse primers. The technique discriminated robustly between mismatches and perfect matches for the 16 indexing sequences tested to allow individual lambda Bcl I fragments to be amplified from their respective adaptor pairs. A strategy is proposed enabling a non-cloning approach to the accession, physical mapping and sequencing of genomic DNA. The method could also have application in high-throughput genetic mapping and fingerprinting and should expand the enzyme base for ligation- mediated indexing technology which has previously been limited to the Class-IIS and IP restriction endonucleases.

Enhanced discrimination of single nucleotide polymorphisms by artificial mismatch hybridization

In order to increase the discrimination of single nucleotide polymorphisms in DNA hybridization, artificial mismatches are inserted into probe oligonucleotides using the base analog 3-nitropyrrole. Differences in thermal stability (delta Tm) between hybrids formed with normal and single-nucleotide-variant DNA targets are increased by as much as 200% over conventional hybridization, and are strongly dependent upon the spacing between mismatches. The increased specificity is demonstrated by hybridization analysis and allele-specific amplification within the HLA-DRB locus.