Chemotaxis in Bacillus subtilis: effects of attractants on the level of methylation of methyl-accepting chemotaxis proteins and the role of demethylation in the adaptation process.

By performing in vivo methylation experiments and using highly resolving NaDodSO4-polyacrylamide gels, we have examined the effects of amino acid attractants on the methylation profile of Bacillus subtilis MCPs. Both increases and decreases have been found to occur in the level of methylation of these proteins. By using competition experiments and Conway diffusion cells, we have found that the demethylation event is correlated with the adaptation process. Gas chromatographic analysis indicates that methanol is evolved upon demethylation of these proteins. As more attractant receptors are titrated, corresponding increases in methanol evolution result. During this period of increased rate of methanol production, bacteria swim smoothly.

Effect of in vitro selenium supplementation on bovine sperm motility.

The effects of selenium (Se) on motility of bovine spermatozoa were evaluated in two experiments. In Experiment 1, increasing doses of Se alone or with vitamin E were found to increase motility in Se concentrations up to 1 mug/ml. However, Se alone had a greater effect than did Se with vitamin E. The sperm motility response to Se concentrations from background to 1 mug/ml on motility best fit a quadratic equation with a maximum at about .65 mug Se/ml. In Experiment 2, the effect of Se addition before and after freezing was evaluated. This experiment demonstrated that treatment of semen with Se before freezing significantly increased the post-thaw motility as compared with portions of the same ejaculate which were not treated. Treatment after thawing produced motilities which were intermediate and not significantly different from either pre-freezing supplementation or no supplementation at all. These data indicate that some semen exhibits a greater percentage of motile sperm when Se is added prior to freezing, however, no information is yet available on the fertility of Se-treated semen.

Secondary structure model for bacterial 16S ribosomal RNA: phylogenetic, enzymatic and chemical evidence.

We have derived a secondary structure model for 16S ribosomal RNA on the basis of comparative sequence analysis, chemical modification studies and nuclease susceptibility data. Nucleotide sequences of the E. coli and B. brevis 16S rRNA chains, and of RNAse T1 oligomer catalogs from 16S rRNAs of over 100 species of eubacteria were used for phylogenetic comparison. Chemical modification of G by glyoxal, A by m-chloroperbenzoic acid and C by bisulfite in naked 16S rRNA, and G by kethoxal in active and inactive 30S ribosomal subunits was taken as an indication of single stranded structure. Further support for the structure was obtained from susceptibility to RNases A and T1. These three approaches are in excellent agreement. The structure contains fifty helical elements organized into four major domains, in which 46 percent of the nucleotides of 16S rRNA are involved in base pairing. Phylogenetic comparison shows that highly conserved sequences are found principally in unpaired regions of the molecule. No knots are created by the structure.