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In vivo in vitro synthesis of ribosomal RNA in bacillus subtilis Webb, Vera Ann B.


The work presented explored the in vivo and in vitro synthesis of ribosomal RNA in the Gram positive, spore-forming bacterium Bacillus subtilis. The investigation began with a study of rRNA synthesis in B. subtilis during steady state growth and under nutritional shift-up conditions. The percent of transcription which is ribosomal RNA was measured by hybridization of pulse labeled RNA to a specific DNA probe carrying the 3' end of the 23S RNA gene. The fractional rate of ribosomal RNA synthesis increased with cellular growth rate, and showed a rapid increase after a nutritional shift up. RNA synthesis during infection with an amber mutant of bacteriophage SP01 was also examined. Infected cells continued to synthesize rRNA at the preinfection rate, but could not respond to media enrichment by increasing the percent rRNA-synthesis. The latter study suggested the existence of a specific RNA polymerase that transcribed ribosomal RNA genes. The conclusions from the in vivo study led to an analysis of rRNA transcription in vitro. The isolation of the putative ribosomal RNA specific RNA polymerase was attempted by affinity chromatography on cellulose complexed with plasmid DNA containing the promoter region of the B. subtilis rrnB rRNA operon, and by sedimentation through a glycerol gradient. No difference in activity profile was observed when transcription activity at the rRNA tandem promoters was compared to activity at a non-ribosomal promoter. Since in vivo analysis of the control of rRNA synthesis in Escherichia coli suggested that regulation occurs at the level of transcription initiation, in vitro transcription initiation at the B. subtilis rRNA promoters was investigated using the single round transcription assay. Initial rates of transcription were different at each of the two tandem promoters of the B. subtilis rrnB operon: the upstream promoter, PI, initiated slowly, while the downstream promoter, P2, initiated faster. In addition, transcription initiation at the two promoters appeared to be linked. The formation of a heparin resistant complex at the PI promoter affected the stability of the heparin resistant complex formed at the P2 promoter. The kinetics of transcription initiation at the tandem rRNA promoters were examined using the tau plot analysis. RNA polymerase had a high affinity for both rRNA promoters, but the rate of initiation at these promoters was relatively slow when compared to non-ribosomal promoters. Finally, transcription initiation on two artificial tandem promoter constructs was compared with initiation on the native tandem promoter construct. In general, PI was shown to have a positive effect on transcription from downstream promoters, but had specific effects on different promoters.

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