FORESPORE EXPRESSION AND PROCESSING OF THE SIGE TRANSCRIPTION FACTOR IN WILD-TYPE AND MUTANT BACILLUS-SUBTILIS

sigma(E) is a mother cell-specific transcription factor of sporulating Bacillus subtilis that is derived from an inactive precursor protein (pro-sigma(E)). To examine the process that prevents sigma(E) activity from developing in the forespore, we fused the sigma(E) structural ge ne (sigE) to forespore-specific promoters (P-dacF and P-spoIIIG), plac ed these fusions at sites on the B. subtilis chromosome which transloc ate into the forespore either early or late, and used Western blot ana lysis to monitor SigE accumulation and pro-sigma(E) processing. sigE a lleles, placed at sites which entered the forespore early, were found to generate more protein product than the same fusion placed at a late entering site. SigE accumulation and processing in the forespore were enhanced by null mutations in spoIIIE, a gene whose product is essent ial for translocation of the distal portion of the B. subtilis chromos ome into the forespore. In other experiments, a chimera of pro-sigma(E ) and green fluorescence protein, previously shown to be unprocessed i f it is synthesized within the forespore, was found to be processed in this compartment if coexpressed with the gene for the pro-sigma(E)-pr ocessing enzyme, SpoIIGA. The need for spoIIGA coexpression is obviate d in the absence of SpoIIIE. We interpret these results as evidence th at selective degradation of both SigE and SpoIIGA prevent mature sigma (E) from accumulating in the forespore compartment of wild-type B. sub tilis. Presumably, a gene(s) located at a site that is distal to the o rigin of chromosome transfer is responsible for this phenomenon when i t is translocated and expressed in the forespore.