Developmental and genetic regulation of bacillus subtilis genes transcribed by σ28-RNA polymerase

Abstract

Sigma-28 RNA polymerase is a minor form of Bacillus subtilis RNA polymerase that is highly specific for transcription from a small number of promoter sites in the B. subtilis genome. We have followed transcription from two of these loci (P 28-1 and P 28-2) in vivo using a quantitative S1 nuclease mapping procedure. Both promoters are used at a modest rate in vegetatively growing cells (about 10 RNA copies per cell) and transcripts are initiated at the same start sites as found in vitro with the purified σ 28-RNA polymerase. Transcription from the σ 28 promoters varies somewhat with growth conditions and is shut off rapidly and almost completely after the first hour of sporulation. Neither σ 28 transcripts is detected in vegetative cells of certain B. subtilis mutants ( spoO classes A, B, E, and F) that are defective in sporulation. Transcription from these promoters is restored in second site revertants that are able to sporulate. Hence the action of σ 28-RNA polymerase appears to be regulated by the spoO genes and the functions controlled by σ 28-promoters may be closely tied to the system involved in the initiation of sporulation.