Effects of plasmid propagation of a sporulation promoter on promoter utilization and sporulation in Bacillus subtilis

Transcription of the sporulation gene spoVG of Bacillus subtilis is induced at the onset of spore formation and depends on the products of the regulatory genes spo0A, spo0B, and spo0H. We describe two effects of propagating the promoter region of spoVG on a multicopy plasmid replicon in B. subtilis cells. One effect is that transcription from the plasmid-borne spoVG promoter is altered with respect to the time of its induction and the dependence on spo0 gene products. An example of this effect is that plasmid propagation was observed to relieve substantially the inhibitory effect of a mutation in spo0H, the spo0 gene upon which spoVG promoter activity is most strongly dependent. We present results which suggest that propagation on a plasmid replicon causes an alteration in the conformation of spoVG promoter DNA which somehow compensates for the defective spo0H gene product. Plasmid propagation did not, however, entirely eliminate the requirement for the spo0H gene product; little or no spoVG-directed RNA synthesis was observed in cells bearing a putative spo0H deletion mutation, a finding which indicates that Spo0H protein plays an indispensable role in spoVG promoter utilization. Another effect of propagating the promoter region of spoVG on a multicopy plasmid is to inhibit sporulation. S1 nuclease mapping experiments suggest that amplification of spoVG on a multicopy plasmid causes the titration of a transcription factor or minor form of RNA polymerase holoenzyme required for utilization of one of the two overlapping promoters which comprise the spoVG transcription initiation region.