Human intestinal anion exchanger isoforms: expression, distribution, and membrane localization

A family of anion exchangers (AEs) including AE1, AE2 and AE3 has been described. AE3 gene has been shown to encode two alternatively spliced isoforms termed as bAE3 (brain subtype) and cAE3 (cardiac subtype). The identity of the AE(s) involved in the human intestinal NaCl absorption is not fully understood. Current studies were undertaken to identify the AE isoforms expressed in the human intestine, to define their regional and vertical axis (crypt vs. surface cells) distribution, and to elucidate their membrane localization in the epithelial cells along the entire length of the human intestine. Our studies utilizing reverse transcription (RT)-PCR with total RNA extracted from pinch biopsies from various regions of the human intestine demonstrate that AE2 and bAE3 but not AE1 or cAE3 were expressed in all the regions of the human intestine. Utilizing in situ RT-PCR, we demonstrated that the message of AE2 was expressed throughout the vertical surface--crypt axis of the colon. Our Western blotting studies demonstrated that AE2 and bAE3 are localized to the basolateral but not the apical membranes of the intestinal epithelial cells from the human ileum and colon. In conclusion, our results demonstrated that in the human intestine, AE2 and bAE3, but not AE1 or cAE3, are expressed throughout the tract with the highest expression in the colon compared to the ileum and jejunum. Both the isoforms were found to be localized to the basolateral but not the apical membranes of the epithelial cells. We speculate that, in the human intestine, AE2 and bAE3 may be the 'housekeeping' isoforms, and the apical AE, the potential candidate for chloride absorption, remains to be identified.

Self-association and mapping of the interaction domain of hepatitis E virus ORF3 protein

Hepatitis E virus (HEV) is a major human pathogen in the developing world. In the absence of an in vitro culture system, very little information on the basic biology of the virus exists. A small protein (approximately 13.5 kDa) of unknown function, pORF3, is encoded by the third open reading frame of HEV. The N-terminal region of pORF3 is associated with the cytoskeleton using one of its hydrophobic domains. The C-terminal half of pORF3 is rich in proline residues and contains a putative src homology 3 (SH3) binding domain and a mitogen-activated protein kinase phosphorylation site. In this study, we demonstrate that pORF3 can homodimerize in vivo, using the yeast two-hybrid system. We have isolated a 43-amino-acid interaction domain of pORF3 which is capable of self-association in vivo and in vitro. The overlap of the dimerization domain with the SH3 binding and phosphorylation domains suggests that pORF3 may have a dimerization-dependent regulatory role to play in the signal transduction pathway.

Bacterial adherence to polymethylmethacrylate posterior chamber intra ocular lenses

PURPOSE

Bacterial adherence to intraocular lenses (IOLs) has been incriminated in the pathogenesis of postoperative endophthalmitis. Staphylococcus epidermidis is the most common organism isolated. We studied the in-vitro adhesion of Staphylococcus epidermidis to Polymethylmethacrylate (PMMA) IOLs and the effect of duration of exposure to adherence.

METHODS

Two groups of 10 IOLs each were incubated in Staphylococcus epidermidis suspension for 2 minutes and 20 minutes respectively. Adhesion of bacterial cells was determined by counting the number of viable bacteria attached to IOLs.

RESULTS

The mean bacterial adherence with 2 minutes incubation was 12,889 +/- 7,150 bacteria/ IOL and with 20 minutes incubation was 84,226 +/- 35,024 bacteria/IOL (P< 0.01).

CONCLUSION

Our results show that Staphylococcus epidermidis adheres to PMMA IOLs in vitro and the degree of adherence is less for shorter duration of exposure. We conclude that viable bacteria irreversibly adherent to IOLs may play a role in the pathogenesis of postoperative endophthalmitis. Shorter duration of operative manipulation and exposure to contaminating sources may decrease the chances of postoperative endophthalmitis.

Real Time PCR Using Molecular Beacons : A New Tool to Identify Point Mutations and to Analyze Gene Expression in Mycobacterium tuberculosis

Molecular beacons are a novel family of hybridization probes, which emit fluorescence upon interaction with their target. They are hairpin-shaped oligonucleotides with a central part complementary to the target, flanked by two 5 6 base pair (bp) inverted repeats, which can form a stable stem. A fluorescent moiety is covalently linked to the 5' end of the molecule, whereas the quenching moiety, 4-(4'-dimethylaminophenylazo)benzoic acid (DABCYL), is covalently linked to the 3' end. The stem keeps the two moieties in close proximity to each other, causing the fluorescence of the fluorophore to be quenched by energy transfer. When molecular beacons bind to their target, they undergo a conformational change that results in the restoration of fluorescence of the internally quenched fluorophore (1) (Fig. 1). Molecular beacons are extremely specific, and can clearly discriminate between targets differing only by a single nucleotide (2,3). When present in a PCR reaction where their target is the amplification product, molecular beacons can form a stable hybrid with the amplicon during the annealing step. The intensity of fluorescence at the annealing step in each amplification cycle is a direct measure of amplicon concentration (2,4) (Fig. 2). Another interesting feature of molecular beacons is that they can be coupled to a variety of differently colored fluorophores. This allows multiplex PCR reactions where different DNA fragments can be amplified and detected simultaneously in the same tube (2,3). Fig. 1. Operation of molecular beacons. On their own, these molecules are nonfluorescent, because the stem hybrid keeps the fluorophore (◯) close to the quencher (•). When the probe sequence in the loop hybridizes to its target, forming a rigid double helix, a conformational reorganization occurs that separates the quencher from the fluorophore, restoring fluorescence (1). Fig. 2. Real time measurement of amplicon synthesis during PCR using molecular beacons. (A) Four PCR reactions were initiated with a different number of template molecules (indicated). The concentration of amplicons present after each cycle of amplification was determined by measuring fluorescence during the last few seconds of the annealing step. (B) Inverted relationship between the threshold cycle (the cycle at which the fluorescent signal becomes detectable above the background) and the logarithm of the initial number of template molecules. In this example, the target is M. tuberculosis H37Rv chromosomal DNA. The primers-molecular beacon set used in the reaction was specific for sigA (reprinted from ref. 4).

Evidence for a Na+-H+ exchange across human colonic basolateral plasma membranes purified from organ donor colons

The mechanism(s) of electrolyte transport across the human colonic contraluminal domain is not well understood. Current studies were undertaken to develop a technique for the isolation and purification of the human colonic basolateral membrane vesicles (BLMV) and to examine the presence of a Na+-H+ exchange process in these membranes. BLMV were purified from mucosal scrapings of organ donor proximal colons utilizing a Percoll density gradient centrifugation technique, and Na+ transport was examined utilizing a rapid filtration, technique. Our data demonstrate that purified basolateral membranes were enriched 10- to 11-fold in Na+, K+-ATPase activity compared to crude homogenate. Results consistent with the Na+-H+ exchange in BLMV are as follows: (1) an outwardly directed H+ gradient stimulated 22Na uptake; (2) 22Na uptake was markedly inhibited by EIPA and amiloride; (3) H+-gradient-stimulated 22Na uptake was not inhibited by bumetanide, SITS, DIDS, acetazolamide, phenamil and benzamil; (4) 22Na uptake was voltage insensitive; (5) 22Na uptake demonstrated saturation kinetics; (6) 22 Na uptake was markedly inhibited by Na+ and Li+ but was unaffected by N-methyl glucamine+, choline+, and NH4+. Immunoblotting studies demonstrated this Na+-H+ exchanger isoform to be represented by NHE1. In conclusion, a technique has been established for the purification of functional human proximal colonic BLMV, and an electroneutral Na+-H+ exchange process has been demonstrated in these membranes.

Combined transformation and genetic technique verification of protein-protein interactions in the yeast two-hybrid system

The yeast two-hybrid system is frequently used to identify protein-protein interactions. The assay is based on the functional reconstitution of a transcriptional activator. Since an indirect phenotype of the positive clones is the basis for selection of positive interacting clones, the two-hybrid screens are vulnerable to false positives. Here we report a screening protocol based on the sequential use of the cotransformation approach followed by the genetic method for verifying true two-hybrid interactions. Using this procedure, we have screened a cDNA library and have been able to isolate true positives from the yeast two-hybrid screen.

C5a-stimulated human neutrophils use a subset of beta2 integrins to support the adhesion-dependent phase of superoxide production

Isolated human polymorphonuclear neutrophils (PMN) responded to human C5a with an immediate, transient release of superoxide lasting from 0.5 to 5 min. This was followed by a second release of superoxide, which began at 10 min after addition of C5a, was sustained for more than 30 min, and required ICAM-1 immobilized in the wells. F(ab')2 monoclonal antibody (mAb) preparations were used to dissect the role of individual beta2 integrins and to avoid the confounding effects of ligating Fc receptors. Anti-CD18 mAb treatment of the PMN had no effect on the immediate first phase but completely inhibited the second, adhesion-dependent phase of superoxide production. Anti-CR3 mAb only inhibited the adhesion phase of superoxide production partially, implying that other beta2 integrins were involved. A mixture of anti-CD11a, anti-CD11b, and anti-CD11c was not able to block superoxide production completely, suggesting a role for alphad/beta2. Surprisingly, blocking anti-LFA-1 mAb had no effect on superoxide production. Consistent with this observation, immobilized, purified ICAM-2, a specific counter-receptor for LFA-1, did not support the adhesion-dependent phase of-superoxide production. Thus, PMN treated with C5a used signals via CR3, P150/95, and alphad/beta2, but not LFA-1, to support superoxide production. LFA-1 has been shown by others to mediate most of the adhesion necessary for transendothelial migration in vivo. The inability of LFA-1 ligation to stimulate superoxide production may be an important means of preventing blood-vessel damage when PMN migrate across the endothelium.

Wavelength-shifting molecular beacons

We describe wavelength-shifting molecular beacons, which are nucleic acid hybridization probes that fluoresce in a variety of different colors, yet are excited by a common monochromatic light source. The twin functions of absorption of energy from the excitation light and emission of that energy in the form of fluorescent light are assigned to two separate fluorophores in the same probe. These probes contain a harvester fluorophore that absorbs strongly in the wavelength range of the monochromatic light source, an emitter fluorophore of the desired emission color, and a nonfluorescent quencher. In the absence of complementary nucleic acid targets, the probes are dark, whereas in the presence of targets, they fluoresce-not in the emission range of the harvester fluorophore that absorbs the light, but rather in the emission range of the emitter fluorophore. This shift in emission spectrum is due to the transfer of the absorbed energy from the harvester fluorophore to the emitter fluorophore by fluorescence resonance energy transfer, and it only takes place in probes that are bound to targets. Wavelength-shifting molecular beacons are substantially brighter than conventional molecular beacons that contain a fluorophore that cannot efficiently absorb energy from the available monochromatic light source. We describe the spectral characteristics of wavelength-shifting molecular beacons, and we demonstrate how their use improves and simplifies multiplex genetic analyses.

Intercellular adhesion molecule 1 and beta2 integrins in C1q-stimulated superoxide production by human neutrophils: an example of a general regulatory mechanism governing acute inflammation

OBJECTIVE

To investigate the role of intercellular adhesion molecule 1 (ICAM-1) and beta2 integrins in the production of superoxide (O2-) by C1q-stimulated human polymorphonuclear leukocytes (PMN).

METHODS

PMN were pretreated with F(ab')2 fragments of monoclonal antibodies (mAb) that blocked or did not block beta2 integrin-mediated adhesion. The cells were added to wells coated with C1q, and the production of O2- was monitored kinetically as a color change due to reduction of cytochrome c. In some experiments, C1q was co-immobilized with purified ICAM-1.

RESULTS

Blocking mAb to the shared beta2 integrin subunit, CD18, completely inhibited the O2- response triggered by immobilized C1q, while blocking mAb to the alpha subunits of the beta2 integrins each partially blocked the O2- response. PMN treated with C1q were found to activate the beta2 integrins lymphocyte function-associated antigen 1 and CR3 for binding to ICAM-1. Co-immobilization of ICAM-1 with C1q cooperatively triggered O2- production by PMN.

CONCLUSION

beta2 integrin binding to an ICAM provided an essential costimulatory signal for O2-production triggered by C1q in PMN. Our findings suggest a model for PMN activation in which 2 stimuli are required for O2- production: a first signal that also activates PMN beta2 integrins, followed by a second, beta2 integrin-mediated signal, which occurs physiologically upon PMN binding to ICAM-1. The requirement for this dual signal for PMN generation of O2- would serve as a regulatory mechanism to limit the production of O2- to a tissue environment where C1q, or some other stimulus, is colocalized with stromal cells bearing up-regulated ICAM-1. This mechanism may explain why all tissues can express ICAM-1 and may explain in part why inhibitors of tumor necrosis factor alpha, a major physiologic stimulus of ICAM-1 up-regulation, are potent antiinflammatory agents.

Rapid identification of Candida dubliniensis using a species-specific molecular beacon

Candida dubliniensis is an opportunistic fungal pathogen that has been linked to oral candidiasis in AIDS patients, although it has recently been isolated from other body sites. DNA sequence analysis of the internal transcribed spacer 2 (ITS2) region of rRNA genes from reference Candida strains was used to develop molecular beacon probes for rapid, high-fidelity identification of C. dubliniensis as well as C. albicans. Molecular beacons are small nucleic acid hairpin probes that brightly fluoresce when they are bound to their targets and have a significant advantage over conventional nucleic acid probes because they exhibit a higher degree of specificity with better signal-to-noise ratios. When applied to an unknown collection of 23 strains that largely contained C. albicans and a smaller amount of C. dubliniensis, the species-specific probes were 100% accurate in identifying both species following PCR amplification of the ITS2 region. The results obtained with the molecular beacons were independently verified by random amplified polymorphic DNA analysis-based genotyping and by restriction enzyme analysis with enzymes BsmAI and NspBII, which cleave recognition sequences within the ITS2 regions of C. dubliniensis and C. albicans, respectively. Molecular beacons are promising new probes for the rapid detection of Candida species.

A DNA damage signal is required for p53 to activate gadd45

We provide direct evidence that overexpression of p53 is not sufficient for robust p53-dependent activation of the endogenous gadd45 gene. When p53 was induced in TR9-7 cells in the absence of DNA damage, waf1/p21 and mdm2 mRNA levels were increased, but a change in gadd45 mRNA was barely detectable. Activation of the gadd45 gene was observed when camptothecin was added to cells containing p53 in the absence of a further increase in the p53 level. Phosphorylation of p53 at serine 15 and acetylation at lysine 382 were detected after drug treatment. It has been suggested that p53 posttranslational modification is critical during activation. However, inhibition of these modifications by wortmannin was not sufficient to block the transactivation of gadd45. Interestingly, after camptothecin treatment, increased DNase I sensitivity was detected at the gadd45 promoter, suggesting that an undetermined DNA damage signal is involved in inducing chromatin remodeling at the gadd45 promoter while cooperating with p53 to activate gadd45 transcription.

Percutaneous transluminal angioplasty for stenosis of the aorta due to aortic arteritis in children

Percutaneous transluminal balloon angioplasty for stenosis of the aorta due to aortic arteritis was attempted on 45 lesions in 41 children (age range, 4-14 years; mean, 9.9+/-4.2 years) presenting with symptoms of hypertension, severe congestive heart failure, and lower limb claudication. Balloon dilatation was technically successful in 38 (92.7%) patients for 41 stenotic lesions (91.1%). The mean peak systolic pressure gradient (PSG) decreased from 71.7 +/- 23.9 mmHg to 23.2 +/- 17.5 mmHg (p < 0.001) and the diameter of the stenosed segment increased from 3.3 +/- 1.1 mm to 7.5 +/- 2.2 mm (p < 0.001) immediately after angioplasty. Patients with short-segment (<3 cm) stenosis had a lower residual gradient (17.9 +/- 11.1 mmHg vs 30.5 +/- 22.6 mmHg; p < 0.05) and a wider diameter of the aorta (8.8 +/- 1.1 mm vs 7.5 +/- 2.2 mm; p < 0.02) compared to patients with long-segment (>/=3 cm) stenosis. Four patients required stent implantation; 2 for flow-limiting dissection, 1 for failure to reduce PSG by >50%, and 1 for recurrent restenosis. There was marked hemodynamic and angiographic improvement in these 4 patients. Hemodynamic and angiographic restudy in 21 of the 41 patients at mean follow-up period of 6.2 +/- 4.2 months (range, 3-24 months) showed restenosis in 4 (19%) patients. Restenosis was more common in patients with long-segment stenosis than those with short-segment stenosis (30% vs 9.1%). Late restudy in 8 patients, done at 3-7 years after first restudy, showed no recurrence of aortic narrowing. On clinical follow-up of 38 patients for a mean of 58.8 +/- 36.0 months (range, 8-146 months) there was marked improvement in symptoms. Hypertension was cured in 11 (29%), improved in 24 (63%), and persisted in 3 (8%). Six patients with associated severe renal artery stenosis showed further improvement in hypertension after successful renal angioplasty. Severe congestive heart failure improved in 21 (95.4%) of 22 patients. Mean left ventricular ejection fraction improved from 0.32 +/- 0.08 to 0. 48 +/- 0.10 (p < 0.001) at a mean follow-up of 28.7 +/- 8.4 months in these patients. Hemodynamic restudy in 10 of these patients showed improvements in left ventricular end-diastolic pressure from a mean 37 +/- 9 mmHg (range, 25-55 mmHg) to 16.4 +/- 6.2 mmHg (range, 6-25 mmHg) (p < 0.001). Lower limb claudication improved in all 4 patients. Our results suggest that percutaneous transluminal balloon angioplasty in children is safe and highly effective in relieving stenosis of the aorta due to aortic arteritis, with marked clinical improvement, and should be the treatment of choice particularly for discrete stenosis.

Endovascular stenting for unsuccessful angioplasty of the aorta in aortoarteritis

PURPOSE

The efficacy and safety of endovascular stent implantation to correct dissection or a suboptimal result after percutaneous transluminal angioplasty (PTA) was evaluated in patients suffering from aortic stenosis due to aortoarteritis.

METHODS

Twelve children and young adults [aged (mean +/- SD) 18.2 +/- 8.7 years] underwent stent implantation after PTA of the aorta, seven for obstructive dissection, four for ineffective balloon dilatation, and one for recurrent restenosis. Nine patients underwent implantation of self-expandable stents and three received balloon-expandable Palmaz stents.

RESULTS

Stent implantation could be successfully performed in all 12 patients. After stent implantation, the peak systolic pressure gradient decreased from 91 +/- 33.5 mmHg to 12.4 +/- 12.5 mmHg (p < 0.001). The diameter of the stenosed segment increased from 4.6 +/- 0.8 mm to 11.1 +/- 1.9 mm (p < 0.001). The dissection was completely covered in all seven patients with dissection. Except for epigastric pain with vomiting in one patient, there was no complication. On follow-up, over 12-57 months (mean 26.8 +/- 10.8 months), 11 patients (91.6%) had marked improvement in their blood pressure. Patients with congestive heart failure and claudication also showed improvement. Repeat catheterization in five patients, between 6-30 months (mean 16.8 +/- 9.1 months) after stent implantation, showed sustained improvement in four and a fusiform, long segment, intrastent restenosis after 30 months in one child. The stenosis was safely redilated.

CONCLUSION

Endovascular aortic stent implantation is safe and provides good immediate relief in patients with unsatisfactory results after balloon angioplasty. Improvement is sustained in most patients on intermediate-term follow-up.

Race-specific HIV-1 disease-modifying effects associated with CCR5 haplotypes

Genetic variation in CC chemokine receptor 5 (CCR5), the major HIV-1 coreceptor, has been shown to influence HIV-1 transmission and disease progression. However, it is generally assumed that the same CCR5 genotype (or haplotype) has similar phenotypic effects in different populations. To test this assumption, we used an evolutionary-based classification of CCR5 haplotypes to determine their associated HIV-1 disease-modifying effects in a large well-characterized racially mixed cohort of HIV-1-seropositive individuals. We demonstrate that the spectrum of CCR5 haplotypes associated with disease acceleration or retardation differs between African Americans and Caucasians. Also, we show that there is a strong interactive effect between CCR5 haplotypes with different evolutionary histories. The striking population-specific phenotypic effects associated with CCR5 haplotypes emphasize the importance of understanding the evolutionary context in which disease susceptibility genes are expressed.

Changing trends in acute poisoning in Chandigarh zone: a 25-year autopsy experience from a tertiary care hospital in northern India

A 25-year autopsy study (1972-1997) of acute poisoning deaths from a tertiary care hospital in northern India (Postgraduate Institute of Medical Education and Research, Chandigarh) revealed a steep increase in the incidence of acute poisoning since 1987. The majority (68%) of subjects were between the ages of 14 and 30 years, and there was a male preponderance (69%). The main victims were students and unemployed youths, followed by agricultural workers and domestic workers. The proportion of urban victims increased from 45% in the period from 1972 to 1977 to 72% in the period from 1992 to 1997. The proportion of suicidal deaths increased from 34% in the period from 1972 to 1977 to 77% in the period from 1992 to 1997, whereas accidental deaths decreased from 63% to 17% in the same period. Barbiturates (37%) and copper sulfate (22%) were the most common poisons causing mortality between 1972 and 1977; organophosphates (46%) became the most common between 1977 and 1982. Since 1982, aluminum phosphide (65%) has been the most common poison.

Expression of the Na+/H+ and Cl-/HCO-3 exchanger isoforms in proximal and distal human airways

Recent studies have indicated the presence of Na+/H+ and Cl-/HCO-3 exchange activities in lung alveolar and tracheal tissues of various species. To date, the identity of the Na+/H+ (NHE) and Cl-/HCO-3 (AE) exchanger isoforms and their regional distribution in human airways are not known. Molecular species of the NHE and AE gene families and their relative abundance in the human airway regions were assessed utilizing RT-PCR and the RNase protection assay, respectively. Organ donor lung epithelia from various bronchial regions (small, medium, and large bronchi and trachea) were harvested for RNA extraction. Gene-specific primers for the human NHE and AE isoforms were utilized for RT-PCR. Our results demonstrated that NHE1, AE2, and brain AE3 isoforms were expressed in all regions of the human airways, whereas NHE2, NHE3, AE1, and cardiac AE3 were not detected. RNase protection studies for NHE1 and AE2, utilizing glyceraldehyde-3-phosphate dehydrogenase as an internal standard, demonstrated that there were regional differences in the NHE1 mRNA levels in human airways. In contrast, the levels of AE2 mRNA remained unchanged. Differential expression of these isoforms in the human airways may have functional significance related to the airway absorption and secretion of electrolytes.

Thermodynamic basis of the enhanced specificity of structured DNA probes

Molecular beacons are DNA probes that form a stem-and-loop structure and possess an internally quenched fluorophore. When they bind to complementary nucleic acids, they undergo a conformational transition that switches on their fluorescence. These probes recognize their targets with higher specificity than probes that cannot form a hairpin stem, and they easily discriminate targets that differ from one another by only a single nucleotide. Our results show that molecular beacons can exist in three different states: bound to a target, free in the form of a hairpin structure, and free in the form of a random coil. Thermodynamic analysis of the transitions between these states reveals that enhanced specificity is a general feature of conformationally constrained probes.

Multiplex detection of four pathogenic retroviruses using molecular beacons

We describe a multiplex nucleic acid assay that identifies and determines the abundance of four different pathogenic retroviruses (HIV-1, HIV-2, and human T-lymphotrophic virus types I and II). Retroviral DNA sequences are amplified in a single, sealed tube by simultaneous PCR assays, and the resulting amplicons are detected in real time by the hybridization of four differently colored, amplicon-specific molecular beacons. The color of the fluorescence generated in the course of amplification identifies which retroviruses are present, and the number of thermal cycles required for the intensity of each color to rise significantly above background provides an accurate measure of the number of copies of each retroviral sequence that were present originally in the sample. Fewer than 10 retroviral genomes can be detected. Moreover, 10 copies of a rare retrovirus can be detected in the presence of 100, 000 copies of an abundant retrovirus. Ninety-six samples can be analyzed in 3 hr on a single plate, and the use of a closed-tube format eliminates crossover contamination. Utilizing previously well characterized clinical samples, we demonstrate that each of the pathogenic retroviruses can be identified correctly and no false positives occur. This assay enables the rapid and reliable screening of donated blood and transplantable tissues.

Stenting of the aorta for recurrent, long stenosis due to Takayasu's arteritis in a child

Balloon angioplasty followed by stenting of the thoracic aorta is reported in a 5-year-old girl with Takayasu's arteritis, who presented with severe hypertension and congestive heart failure. Her aortogram showed severe long segment stenosis of the descending thoracic aorta, which was successfully treated by balloon angioplasty on two occasions, but developed recurrences after 6 and 7 months of angioplasty. Balloon dilatation of the stenosed aorta, followed by sequential implantation of three 30-mm long Palmaz stents in tandem, bridging the full segment of the angioplastied aorta were performed successfully without any complications. The aortic diameter increased from 3.3 mm to 7.7 mm and the peak systolic pressure gradient decreased from 75 mmHg to 3 mmHg. There was no recurrence on clinical follow-up of 13 months.

Multiplex detection of single-nucleotide variations using molecular beacons

We demonstrate that single-nucleotide differences in a DNA sequence can be detected in homogeneous assays using molecular beacons. In this method, the region surrounding the site of a sequence variation is amplified in a polymerase chain reaction and the identity of the variant nucleotide is determined by observing which of four differently colored molecular beacons binds to the amplification product. Each of the molecular beacons is perfectly complementary to one variant of the target sequence and each is labeled with a different fluorophore. To demonstrate the specificity of these assays, we prepared four template DNAs that only differed from one another by the identity of the nucleotide at one position. Four amplification reactions were prepared, each containing all four molecular beacons, but each initiated with only one of the four template DNAs. The results show that in each reaction a fluorogenic response was elicited from the molecular beacon that was perfectly complementary to the amplified DNA, but not from the three molecular beacons whose probe sequence mismatched the target sequence. The color of the fluorescence that appeared in each tube during the course of the amplification indicated which nucleotide was present at the site of variation. These results demonstrate the extraordinary specificity of molecular beacons. Furthermore, the results illustrate how the ability to label molecular beacons with differently colored fluorophores enables simple multiplex assays to be carried out for genetic analysis.

Differential expression of 10 sigma factor genes in Mycobacterium tuberculosis

The ability of Mycobacterium tuberculosis to adapt to different environments in the infected host is essential for its pathogenicity. Consequently, this organism must be able to modulate gene expression to respond to the changing conditions it encounters during infection. In this paper we begin a comprehensive study of M. tuberculosis gene regulation, characterizing the transcript levels of 10 of its 13 putative sigma factor genes. We developed a real-time RT-PCR assay using a family of novel fluorescent probes called molecular beacons to quantitatively measure the different mRNAs. Three sigma factor genes were identified that have increased mRNA levels after heat shock, two of which also responded to detergent stress. In addition, we also identified a sigma factor gene whose mRNA increased after mild cold shock and a second that responded to conditions of low aeration.