In vitro transcription of a late class of phage SP01 genes

Abstract

Bacillus subtilis phage SP01 directs the synthesis of at least six temporally defined classes of phage-specified transcripts¹. Synthesis of the two earliest classes of phage RNA (e and em) does not require phage protein synthesis, while the synthesis of middle (m and m₁l) and late (m₂l and l) transcripts requires the protein product of regulatory gene 28 and the products of regulatory genes 33 and 34, respectively^2,3. The discovery of SP0l-induced polypeptides associated with B. subtilis RNA polymerase suggested that the products of SP01 regulatory genes could control transcription by interacting directly with the host RNA polymerase^4,5. In support of this idea, we reported⁶ that a form of RNA polymerase from SP01-infected cells copies middle RNA almost exclusively from the heavy (H) strand of native SP01 DNA, the DNA strand from which middle and late genes are transcribed in vivo. This enzyme contains an SP01-induced polypeptide termed IV (molecular weight 26,000) that is now known to be the product of regulatory gene 28 (T. Fox, R. L. and J. P., manuscript in preparation). Accurate middle gene transcription by this phage-modified RNA polymerase does not require σ factor but is apparently dependent on a newly described host subunit of RNA polymerase called δ (molecular weight 21,500)⁶. Other workers have also reported the preferential synthesis of middle RNA by RNA polymerase from phage-infected B. subtilis^7,8. Here we report that in the presence of host δ protein a form of RNA polymerase containing phage-induced polypeptides termed V (molecular weight 24,000) and VI (molecular weight 13,500) asymmetrically transcribes a class of SP01 late genes in vitro.