Activation of a cryptic gene by excision of a DNA fragment.

The cryptic bgl operon in Escherichia coli K-12 strain 1011A contains a 1.4-kilobase-pair fragment of foreign DNA within the bglF structural gene. The active allele found in its descendant strain, MK1, required the precise excision of that insertion for its activation. Molecular and genetic approaches have shown that strain 1011A possessed an active (bglR+) rather than a silent wild-type (bglR0) allele of the regulatory region and that this change was caused by a point mutation. Our model for the retention of cryptic genes (B. G. Hall, S. Yokoyama, and D. H. Calhoun, Mol. Biol. Evol. 1:109-124, 1983) suggested that the insertion might have been selected to silence a disadvantageous bglR+ allele. We examined the genealogy of strain MK1 and found that the insertion of foreign DNA was not selected for that reason, since it preceded the change to bglR+. This means that the change to bglR+ was also not selected, since the presence of the insertion would not allow expression of the operon. We have calculated the probability of isolating a bglR+ mutation by chance alone as less than 10(-8). We suggest that mutation rates estimated under the usual conditions of exponential growth may be irrelevant to the frequencies of these events under natural conditions.     

Mechanism of androstenedione formation from testosterone and epitestosterone catalyzed by purified cytochrome P-450b

A purified rat hepatic monooxygenase system containing cytochrome P-450b oxidizes testosterone to androstenedione and 16 alpha- and 16 beta-hydroxytestosterone at approximately equal rates. The metabolism of epitestosterone by the same system is characterized by a marked stereoselectivity in favor of 16 beta-hydroxylation (4- to 5-fold relative to 16 alpha-hydroxylation), formation of 15 alpha-hydroxyepitestosterone, and a rate of androstenedione formation which is three to five times higher than that observed with testosterone. Apparent Km values for 16 alpha- and 16 beta-hydroxylation and androstenedione formation are 20-30 microM with either substrate. Mass spectral analysis of the androstenedione formed from [16,16-2H2]testosterone and [16,16-2H2] epitestosterone indicates essentially complete retention of deuterium, thereby ruling out a mechanism of androstenedione formation via C-16 hydroxylation followed by loss of water and rearrangement. Mass spectral analysis of the C-16 hydroxylation products from incubations of testosterone or epitestosterone in 18O2 shows essentially complete incorporation of 18O (greater than 95%). Androstenedione formed from testosterone is enriched in 18O only 2-fold (5-8%) over background, while the androstenedione formed from epitestosterone shows 84% enrichment. Kinetic experiments utilizing [17-2H]testosterone and [17-2H]epitestosterone as substrates indicate that cleavage of the C-17 carbon-hydrogen bond is involved in a rate-limiting step in the formation of androstenedione from both substrates. Taken together, our results indicate that androstenedione formation from epitestosterone proceeds exclusively through the gem-diol pathway, while androstenedione formation from testosterone may proceed through a combination of gem-diol and dual hydrogen abstraction pathways.     

Amino acid substitutions in mitochondrial ATPase subunit 9 of Saccharomyces cerevisiae leading to oligomycin or venturicidin resistance

A series of isonuclear oligomycin-resistant mutants of Saccharomyces cerevisiae carrying mutations in the mitochondrial oli1 gene has been studied. DNA sequence analysis of this gene has been used to define the amino acid substitutions in subunit 9 of the mitochondrial ATPase complex. A domain of amino acids involved in oligomycin resistance can be recognized which encompasses residues in each of the two hydrophobic portions of the subunit 9 polypeptide that are thought to span the inner mitochondrial membrane. Certain amino acid substitutions also confer cross-resistance to venturicidin: these residues define an inner domain for venturicidin resistance. The expression of venturicidin resistance resulting from one particular substitution is modulated by nuclear genetic factors.     

Purification to homogeneity of aromatase from human placenta

Aromatase cytochrome P-450 has been purified from human placenta to homogeneity, as demonstrated by electrophoresis on polyacrylamide gels with SDS, and by double diffusion against an antibody raised in rabbits. The enzyme converts androstenedione to estrone (Vmax 13.3 n moles/min/n mole P-450; Km 30 microM) and testosterone to estradiol. Aromatase activity requires P-450, P-450 reductase and NADPH. Enzyme activity is inhibited by anti-aromatase antibodies and by 4-hydroxyandrostenedione. The enzyme shows a molecular weight of 55,000, is extremely unstable and spontaneously forms P-420 with a half-life of 2.5 days.     

In nondividing cells, histone H1(0) is synthesized and deposited onto chromatin without accompanying phosphorylation

The phosphorylation of H1 histone subfractions was measured in mouse neuroblastoma cells stopped from dividing by three treatments that block cell division: 5 mM butyrate, 2% dimethyl sulfoxide, and serum withdrawal. H1 histone phosphorylation decreased in response to all three treatments, but the response differed in its timing and its extent for the different H 1 subfractions. The different decreases in phosphorylation correlated well with the differential decreases in biosynthesis of the individual H1 subfractions; however, an exception to this parallel decrease in synthesis and phosphorylation was observed in the case of histone H1(0). Phosphorylation of H1(0) was absent in each of the three treatments after 2 days, despite the continued synthesis and deposit of H1(0) on the chromatin. Thus, despite the fact that H1(0) was being synthesized and that the other newly synthesized H1 subfractions were phosphorylated at this time, the phosphorylation of H1(0) became uncoupled from its synthesis after prolonged treatments blocking cell division.     

Distribution and application of mycobactins for the characterization of species within the genus Rhodococcus

Representatives of 11 species of Rhodococcus were examined for their ability to synthesize mycobactin, a lipid-soluble siderophore, following iron-limited growth on solidified glycerol/asparagine medium. Rhodococcus bronchialis, R. terrae and R. rubropertinctus formed mycobactins, whereas the remaining species (R. coprophilus, R. equi, R. erythropolis, R. rhodnii, R. rhodochrous, R. ruber, R. maris and R. luteus) failed to synthesize these compounds even under conditions of strictly iron-limited growth. The mycobactins from R. terrae and R. rubropertinctus showed close similarity by thin-layer chromatography and high-performance liquid chromatography and could be easily distinguished from that of R. bronchialis.     

A cooperative taxonomic study of mycobacteria isolated from armadillos infected with Mycobacterium leprae

Seventeen strains of mycobacteria, recovered from six armadillos experimentally infected with Mycobacterium leprae, were examined in ten different laboratories. This collaborative study included use of conventional bacteriological tests, lipid analyses, determination of mycobactins and peptidoglycans, characterization by Py-MS, and immunological, metabolic, pathological and DNA studies. These armadillo-derived mycobacteria (ADM) formed five homogeneous groups (numbered ADM 1 to 5) on the basis of phenetic analyses. However, DNA studies revealed only four homogeneous groups since group ADM 1 and one of the two strains in group ADM 3 showed a high level of DNA relatedness. The phenetic and DNA studies confirmed that the ADM strains differed from all other known mycobacteria. Cultural, biochemical, metabolic and pathogenic properties as well as DNA-DNA hybridizations clearly differentiated these ADM from M. leprae.     

A study of anti-group A streptococcal monoclonal antibodies cross-reactive with myosin

Anti-group A streptococcal monoclonal antibodies were obtained from BALB c/BYJ mice immunized with purified membranes from M type 5 Streptococcus pyogenes. Two of the anti-streptococcal monoclonal antibodies were previously shown to cross-react with muscle myosin. In this study the monoclonal antibodies were reacted with tissue sections of normal human heart and skeletal muscle. Antibody binding was estimated by indirect immunofluorescence and immunoperoxidase techniques. Both of the monoclonal antibodies (36.2.2 and 54.2.8) investigated in this report reacted with heart and/or skeletal muscle sections. When evaluated by immunofluorescence, monoclonal antibody 54.2.8 demarcated the periphery of cardiac striated muscle cells and reacted to a lesser degree with subsarcolemmal components. Monoclonal antibody 36.2.2 failed to react with heart sections, but both of the monoclonal antibodies reacted strongly with skeletal muscle sections. Results similar to those observed with indirect immunofluorescence were obtained with the immunoperoxidase technique. By Western immunoblotting and competitive inhibition assays, monoclonal antibodies 36.2.2 and 54.2.8 both were found to react with the heavy chain of skeletal muscle myosin. However, only 54.2.8 reacted with the heavy chain of cardiac myosin. The specificity of the monoclonal antibodies for subfragments of skeletal muscle myosin indicated that monoclonal antibody 36.2.2 was specific for light meromyosin fragments, whereas 54.2.8 reacted with both heavy and light meromyosin. The data demonstrated that two monoclonal antibodies against streptococci were specific for skeletal muscle and/or cardiac myosin and for subfragments of the myosin molecule. The reactions of the monoclonal antibodies with human tissue sections were consistent with the immunochemical reactions of the monoclonal antibodies with both denatured and native myosin.     

Evaluation of the control of Myobia musculi infestations on laboratory mice with permethrin

The efficacy of permethrin against Myobia musculi (Schrank) (Acari:Myobiidae) infestations on mice was evaluated using four different dose delivery methods. In all methods, an attempt was made to deliver 0.5 mg of active permethrin weekly to each mouse. Successful control was achieved with topical or environmental treatment with 0.25% permethrin dust and by dipping the mice into a 0.6 g/l permethrin emulsion. The use of an emulsion applied to the bedding produced the least satisfactory control. Untreated mice had an average infestation rate of 57.3% throughout the study. No significant differences were seen between treated and untreated groups in either body weight or histopathology of the liver, lung, or kidney.