SummaryStaphylococcus aureus is a potent human pathogen that expresses a large number of virulence factors in a temporally regulated fashion. Two pleiotropically acting regulatory loci were identi®ed in previous mutational studies. The agr locus comprises two operons that express a quorum-sensing system from the P2 promoter and a regulatory RNA molecule from the P3 promoter. The sar locus encodes a DNA-binding protein that activates the expression of both agr operons. We have cloned the sarA gene, expressed SarA in Escherichia coli and puri®ed the recombinant protein to apparent homogeneity. The puri®ed protein was found to be dimeric in the presence and absence of DNA and to consist mostly of a-helices. DNase I footprinting of SarA on the putative regulatory region cis to the agr promoters revealed three high-af®nity binding sites composed of two half-sites each. Quantitative electrophoretic mobility shift assays (EMSAs) were used to derive equilibrium binding constants (K D ) for the interaction of SarA with these binding sites. An unusual ladder banding pattern was observed in EMSA with a large DNA fragment including all three binding sites. Our data indicate that SarA regulation of the agr operons involves binding to multiple halfsites and may involve other sites located downstream of the promoters.

Comparison of Staphylococcus aureus strains carrying mutations inactivating the staphylococcal accessory regulator (sar ) and/or the accessory gene regulator (agr ) suggests that sar is the primary regulatory element controlling transcription of the collagen adhesin gene (cna ) and that the regulatory effect of sar is independent of the interaction between SarA and agr. To test this hypothesis, we cloned the regions encoding each of the overlapping sar transcripts, all of which include the sarA open reading frame (ORF), and introduced each clone into cna‐positive sar and agr mutants. The introduction of each clone restored the expected sar transcripts and the temporal pattern of sar transcription. The introduction of each clone also complemented the defect in cna transcription and restored collagen binding to wild‐type levels. This was true even when the clones were introduced into a sar/agr double mutant. These results confirm the hypothesis that the sar‐mediated regulation of cna transcription occurs via an agr‐independent pathway. Direct evidence supporting this hypothesis comes from electrophoretic mobility shift assays demonstrating that SarA exhibits high‐affinity binding to cis elements upstream of the cna structural gene. We also examined the correlation between sar transcription and the production of SarA. Western blot analysis of two wild‐type strains indicated that SarA was produced in indistinguishable amounts during both the exponential and the post‐exponential growth phases.

In this study the possible role of human papillomaviruses (HPV) in spontaneous abortions is addressed by assaying for HPV DNA in first trimester spontaneous and electively aborted products of conception materials enriched for chorionic villi. The presence of HPVs was measured by polymerase chain reaction (PCR) amplification and DNA dot blot hybridization using an internal probe. The "broad spectrum" HPV primers were directed to amplify E6/E7 junction sequences, while the probe was of an HPV-16 sequence with significant homology to HPV-6/11. The quantity and quality of isolated DNA was also analyzed and compared by observing the PCR amplification of a cellular sequence from the human beta-globin gene. Fifteen of the 25 spontaneous samples (60%) were found to be positive for HPV E6/E7 sequences. In comparison, only 3 of the 15 elective samples (20%) were positive. This is the first study of HPV in fetal materials to incorporate material from elective abortions as a control group. Although confounding contamination from the cervix and vagina can't be ruled out, these data are significant and strongly suggest that HPVs are elevated in spontaneously aborted products of conception. Furthermore, these results suggest the possibility that HPVs may be etiologic agents of at least some spontaneous abortions.

The molecular basis for the treatment of human herpesviruses with nucleoside drugs is the phosphorylation of these drugs by the viral-encoded thymidine kinases. In order to better understand the structural and enzymatic mechanisms by which herpesviral thymidine kinases recognize their substrates, photoaffinity labeling with [alpha-32P]5-azido-2'-deoxyuridine-5'-monophosphate and [ gamma-32P]8-azidoadenosine-5'-triphosphate was used to characterize the thymidine, thymidylate, and ATP active sites of the herpes simplex virus-1 (HSV-1) thymidine kinase. For this study, HSV-1 thymidine kinase and a site-specific mutant enzyme (C336Y, known to confer acyclovir resistance) were expressed in bacteria and purified by a rapid, two-step protocol. The specificity of photoaffinity labeling of these HSV-1 thymidine kinases was demonstrated by the ability of site-directed substrates such as thymidine, thymidylate, acyclovir, 5-bromovinyl-2'-deoxyuridine, and ATP to inhibit photoinsertion. Differences in inhibition patterns of photoaffinity labeling correlated with kinetic differences between the wild-type and C336Y HSV-1 thymidine kinases. Cumulative results suggest that the acyclovir-resistant cysteine 336 mutation primarily affects the ATP binding site; yet it also leads to alteration in the binding affinity of nucleoside drugs in the thymidine site. In this study, azidonucleotide photoaffinity analogs are shown to be effective tools for studying the active-site environment of HSV-1 thymidine kinase and related site-specific mutants.

No abstract