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In Vitro Activity of a Novel Diaminopyrimidine Compound, Iclaprim, against Chlamydia trachomatis and C . pneumoniae. S. A. Kohlhoff, 2004.The in vitro activities of iclaprim, a novel dihydrofolate reductase inhibitor, azithromycin, and levofloxacin were tested against 10 strains of Chlamydia trachomatis and 10 isolates of Chlamydia pneumoniae . For C . trachomatis and C . pneumoniae, the iclaprim MIC and minimal bactericidal concentration at which 90% of isolates were inhibited (MIC90 and MBC90) were 0.5 µg/ml, compared to an azithromycin MIC90 and MBC90 of 0.125 µg/ml and levofloxacin MIC90s and MBC90s of 1 µg/ml for C . trachomatis and 0.5 µg/ml for C . pneumoniae . Genetic Loci for Coaggregation Receptor Polysaccharide Biosynthesis in Streptococcus gordonii 38. De-Qi Xu, 2003.The cell wall polysaccharide of Streptococcus gordonii 38 functions as a coaggregation receptor for surface adhesins on other members of the oral biofilm community . The structure of this receptor polysaccharide (RPS) is defined by a heptasaccharide repeat that includes a GalNAcß1  3Gal-containing recognition motif . The same RPS has now been identified from S . gordonii AT, a partially sequenced strain . PCR primers designed from sequences in the genomic database of strain AT were used to identify and partially characterize the S . gordonii 38 RPS gene cluster . This cluster includes genes for seven putative glycosyltransferases, a polysaccharide polymerase (Wzy), an oligosaccharide repeating unit transporter (Wzx), and a galactofuranose mutase, the enzyme that promotes synthesis of UDP-Galf, one of five predicted RPS precursors . Genes outside this region were identified for the other four nucleotide-linked sugar precursors of RPS biosynthesis, namely, those for formation of UDP-Glc, UDP-Gal, UDP-GalNAc, and dTDP-Rha . Two genes for putative galactose 4-epimerases were identified . The first, designated galE1, was identified as a pseudogene in the galactose operon, and the second, designated galE2, was transcribed with three of the four genes for dTDP-Rha biosynthesis (i.e., rmlA, rmlC, and rmlB) . Insertional inactivation of galE2 abolished (i) RPS production, (ii) growth on galactose, and (iii) both UDP-Gal and UDP-GalNAc 4-epimerase activities in cell extracts . Repair of the galE1 pseudogene in this galE2 mutant restored growth on galactose but not RPS production . Cell extracts containing functional GalE1 but not GalE2 contained UDP-Gal 4-epimerase but not UDP-GalNAc 4-epimerase activity . Thus, provision of both UDP-Gal and UDP-GalNAc for RPS production by S . gordonii 38 depends on the dual specificity of the epimerase encoded by galE2 .
tRNA2Thr Complements Temperature Sensitivity Caused by Null Mutations in the htrB Gene in Escherichia coli. Yoshio Mohri, 2003.According to the wobble rule, tRNA2Thr is nonessential for protein synthesis, because the codon (ACG) that is recognized by tRNA2Thr is also recognized by tRNA4Thr . In order to investigate the reason that this nonessential tRNA nevertheless exists in Escherichia coli, we attempted to isolate tRNA2Thr-requiring mutants . Using strain JM101F-, which lacks the gene for tRNA2Thr, we succeeded in isolating two temperature-sensitive mutants whose temperature sensitivity was complemented by introduction of the gene for tRNA2Thr . These mutants had a mutation in the htrB gene, whose product is an enzyme involved in lipid A biosynthesis . Although it is known that some null mutations in the htrB gene give a temperature-sensitive phenotype, our mutants exhibited tighter temperature sensitivity . We discuss a possible mechanism for the requirement for tRNA2Thr .
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