BACILLUS-SUBTILIS LON PROTEASE PREVENTS INAPPROPRIATE TRANSCRIPTION OF GENES UNDER THE CONTROL OF THE SPORULATION TRANSCRIPTION FACTOR SIGMA(G)

The Bacillus subtilis RNA polymerase sigma factor sigma(G) is a cell-t ype-specific regulatory protein that governs the transcription of gene s that are expressed at an intermediate to late stage of sporulation i n the forespore compartment of the sporangium. Here we report the iden tification of a mutation (ion-1) that causes inappropriate transcripti on of genes under the control of sigma(G) under nutritional and geneti c conditions in which sporulation is prevented. The mutation is locate d at 245 degrees on the genetic map and lies within a newly identified open reading frame that is predicted to encode a homolog to Lon prote ase. Inappropriate transcription of sigma(G)-controlled genes in the l on-1 mutant is not prevented by mutations in genes that are normally r equired for the appearance of sigma(G) during sporulation but is preve nted by a mutation in the structural gene (spoIIIG) for sigma(G) itsel f. In light of previous work showing that spoIIIG is subject to positi ve autoregulation, we propose that a Lon protease is responsible (poss ibly by causing degradation of sigma(G)) for preventing sigma(G)-direc ted transcription of spoIIIG and hence the accumulation of sigma(G) in cells that are not undergoing sporulation, An integrated physical and genetic map is presented that encompasses 36 kb of uninterrupted DNA sequence from the ion pheA region of the chromosome, corresponding to 245 degrees to 239 degrees on the genetic map.