Transcriptional specificity of a multisubunit RNA polymerase induced by Bacillus subtilis bacteriophage PBS2.

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RESUMO

Bacillus subtilis phage PBS2 induced the synthesis of two temporally defined categories of phage-specified transcripts. The transcription of phage "early" genes was induced almost immediately after infection; this RNA synthesis did not require phage protein synthesis. Phage "late" gene transcription, on the other hand, was induced at an intermediate time in the lytic cycle; this RNA synthesis required the production of phage proteins. Both classes of transcription were resistant to the drug rifampin and, therefore, apparently did not require the rifampin-sensitive component of the host RNA polymerase. A rifampin-resistant, DNA-dependent RNA polymerase was purified from bacteria infected with PBS2. The highly purified phage polymerase consisted of five distinct subunits that remained associated during zone centrifugation, isoelectric focusing, and disc gel electrophoresis. The synthesis of each of the five polypeptides was induced at an intermediate time in the phage lytic cycle. As judged by hybridization competition, hybridization to DNA restriction fragments, and RNA-RNA annealing, the phage-induced RNA polymerase preferentially and asymmetrically transcribed PBS2 late genes in vitro. These findings suggest that the PBS2 RNA polymerase controls the expression of phage genes late in the lytic cycle.

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