Biomedical subjects
Publications and source records attributed to S H Larsen.
16-Deethylindanomycin (A83094A) is a novel pyrrole-ether antibiotic produced by a strain of Streptomyces setonii. The antibiotic, which is structurally similar to indanomycin (X-14547A), is active in vitro against Gram-positive bacteria as well as coccidia.
Analysis of two agnogene mutants, dl2304 deleted over the entire agnogene and in2379 carrying a 2-base insert, indicated that the mutant phenotype of small plaque formation must be the result of a defect late in the maturation pathway. Both mutants were removed from the pool of molecules available for replication with wild-type kinetics. Whereas dl2304 was somewhat reduced in its rate of progression from chromatin to previrions-virions, in2379, which produced even smaller plaques than dl2304 did, progressed with wild-type kinetics. Therefore, the agnoprotein was not required for progression from chromatin to previrions.
We report the identification and partial sequence for a human salivary amylase gene, Amy1. The genomic sequence was compared with known human pancreatic and salivary amylase cDNA sequences and another salivary amylase gene sequence. While most of the intron/exon structure and coding sequences are highly similar to other amylase DNAs, the bulk of the 5' end varies significantly. Major differences in the positions and structures of promoters between human and mouse Amy1 genes suggest that there are important differences between the tissue-specific expressions in the two mammals. Some potential enhancer sequences were identified.
A nucleic acid spot hybridization assay was used to detect Chlamydia trachomatis DNA. The hybridization probes included DNA isolated from elementary bodies of lymphogranuloma venereum (LGV) strains and cloned fragments of both chromosomal and plasmid DNA. The sensitivity of the test was in the range 10 to 100 pg homologous DNA and 10 in vitro infected cells. Cross-reactivity with bacterial DNA was avoided when purified chlamydia-specific DNA fragments were used as probes. C. trachomatis was detectable in most of the clinical specimens with large amounts of infectious particles. Also some isolation-negative specimens gave a positive signal in the test.
Pulse-labeled simian virus 40 (SV40) DNA is removed from the pool of molecules available for replication (i.e., it ceases to reenter replication) a few hours after synthesis. We studied this cessation of reentry with mutants containing different deletions in the structural genes of SV40. The DNAs of two independent deletion mutants, dl-1007 (24% deletion) and dl-1003 (8% deletion), were used as templates for further DNA synthesis (i.e., they reentered replication) to a greater extent than was wild-type DNA. The alteration in reentry kinetics was not because the DNAs were smaller; other deletion mutations that were from 76 to 85% of the length of wild-type DNA (dl-BE and dl-1133 with a deletion in the late region and F8dl with a deletion in the early region) did not reenter replication to a greater extent than the wild type did. Cotransfection experiments showed that the mutant phenotypes of dl-1007 and dl-1003 were poorly complemented, if at all, by the wild type. Thus, we propose that there is a cis-acting sequence located in the HindIII E fragment of SV40, not present in either of these mutants, that promotes the efficient removal of DNA from the replication pathway.
Elementary bodies of lymphogranuloma venereum (LGV) strains of Chlamydia trachomatis contain, in addition to the genomic DNA, a 6.7 kb plasmid. The plasmid from serovar L2 (434-B) was cloned at the BamHI site of pBR327 into Escherichia coli and a restriction cleavage map of this pLGV125 recombinant plasmid determined. All 15 C. trachomatis serovars contained DNA sequences that hybridized with pLGV125. When total DNA from L2 elementary bodies was used as a probe in Southern blotting and spot hybridization, serovars L1, L2 and L3 exhibited significant homology. The detection level of homologous DNA was 100 pg and LGV DNA was detectable in infected cells when total L2 probe was used in the nucleic acid hybridization test. These DNA probes may be useful as investigative and diagnostic reagents for C. trachomatis.
We report the nucleotide sequence of mRNA for the common electrophoretic isozyme of human pancreatic alpha-amylase, Amy2 A. The sequence was derived from a nearly full-length complementary DNA (cDNA) isolated from a cloned cDNA library. The relatively short 5' untranslated region (15 nucleotides) was determined by primer-extension sequencing. The human Amy2 messenger codes for a 511-residue preamylase polypeptide. An amino-terminal signal peptide of 15 amino acids with an Ala X Gln cleavage site is proposed based on homology to mouse, dog and hog amylases. The Amy2 A mRNA sequence differs from a recently reported human Amy2 sequence. Differences were found at 31 nucleotide positions. The alpha-amylase proteins predicted by the two mRNAs differ at 17 amino acid positions. Relative to the known sequences of other mammalian amylases, most of the differences between the two human Amy2 sequences appear to have occurred as substitutions in the sequence reported by Nakamura et al. (1984). These substitutions predict a protein with a substantially greater net negative charge than that of Amy2 A. We suggest that the two sequences may represent either divergent Amy2 alleles or the expression of non-allelic pancreatic amylase genes.
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A protein methylation reaction involved in chemotaxis of Escherichia coli has been identified. The involvement of this reaction in chemotaxis in indicated by four lines of evidence. (a) The methylation reaction is altered in several classes of generally nonchemotactic mutants and is coreverted with the chemotaxis defects. (b) The methylation level of the protein is affected by chemotactic stimuli. (c) The transferred methyl group is derived from methionine and is labile, in accord with the known fact that chemotaxis requires a continuous supply of methionine. (d) Methylation is abnormal in various mutants having defective or missing flagella.
Chemotactic responses are mediated by modulation of the frequency of tumbling. Studies with methionine auxotrophs of wild-type Escherichia coli and four mutants which tumble continuously show that methionine or one of its metabolites is involved in the tumbling process. Following removal of methionine, the wild type and two mutants, after various periods of time, became unable to tumble. The presence of constant levels of chemical attractants considerably shortened these periods in the three strains and eliminated tumbling in another mutant. This effect of attractants considerably shortened these periods in the three strains and eliminated tumbling in another mutant. This effect of attractants implies that methionine or some derivative of methionine is also involved in transducing chemical stimuli to bacterial responses.
A novel group of antibiotics, comprising microbiologically-active structurally-related factors A25822A, B, D, H, L, M and N, produced by culturing Geotrichum flavo-brunneum NRRL 3862 under submerged aerobic fermentation conditions was isolated by extraction. The individual factors were separated and purified by chromatography and crystallization. The major factor, A25822B, a 15-aza-24-methylene-D-homocholestadiene is a white crystalline compound, C25H45NO. The antibiotics are highly active against fungi and marginally active against bacteria.
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The source of energy for bacterial motility is the intermediate in oxidative phosphorylation, not ATP directly. For chemotaxis, however, there is an additional requirement, presumably ATP. These conclusions are based on the following findings. (i) Unlike their parents, mutants of Escherichia coli and Salmonella typhimurium that are blocked in the conversion of ATP to the intermediate of oxidative phosphorylation failed to swim anaerobically, even when they produced ATP. When respiration was restored to the mutants, motility was simultaneously restored. (ii) Carbonylcyanide m-chlorophenylhydrazone, which uncouples oxidative phosphorylation, completely inhibited motility even though ATP remained present. (iii) Arsenate did not inhibit motility in the presence of an oxidizable substrate, though it did reduce ATP levels to less than 0.3% (iv) Arsenate completely inhibited chemotaxis under conditions where motility was normal.
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