Below the promoters are SigA and SigN consensus sequences with vertical lines to indicate a consensus match. Boxes surround −35 and −10 regions relative to the +1 transcriptional start site. Promoter regions are indicated by brackets. (A) A schematic of the promoter region of sigN. LexA RNA polymerases RNAP cell death plasmid plasmids sigma factor sigma factors. Here, we report the presence of a sigma factor that is encoded on a plasmid that leads to cellular death after DNA damage. Some sigma factors are activated during times of stress to ensure the survival of the bacterium. IMPORTANCE Sigma factors are utilized by bacteria to control and regulate gene expression. How cells die in a pBS32-dependent manner remains unknown, but we predict that death is the product of expressing one or more genes in the SigN regulon. Thus, in response to DNA damage SigN is derepressed and then experiences positive feedback. Finally, we characterize the regulation of SigN itself and show that it is transcribed by at least three promoters: P sigN1, a strong SigA-dependent LexA-repressed promoter P sigN2, a weak SigA-dependent constitutive promoter and P sigN3, a SigN-dependent promoter. Rend-seq (end-enriched transcriptome sequencing) analysis was used to determine the SigN regulon on pBS32, and the 5' ends of transcripts were used to predict the SigN consensus sequence. Here, we show that ZpdN is a bona fide sigma factor that can direct RNA polymerase to transcribe ZpdN-dependent genes, and we rename ZpdN SigN accordingly. DNA damage triggers pBS32 hyperreplication and cell death in a manner that depends on ZpdN, but how ZpdN mediates these effects is unknown. subtilis also encodes an additional sigma factor homolog, ZpdN, not found in lab strains due to being encoded on the large, low-copy-number plasmid pBS32, which was lost during domestication. Laboratory strains of Bacillus subtilis encode many alternative sigma factors, each dedicated to expressing a unique regulon such as those involved in stress resistance, sporulation, and motility.

Sigma sign