Differential gene expression during sporulation in Bacillus subtilis: structure and regulation of the spoIIID gene

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Abstract
The gene spoIIID, which is essential for spore formation in Bacillus subtilis, was cloned and sequenced. It consists of one open reading frame which would encode a 93‐amino‐acid protein with a classic helix‐turn‐helix motif, characteristic of sequence‐specific DNA‐binding proteins. SpoIIID protein is a previously identified transcription factor, capable of altering the specificity of RNA polymerase containing sigma K in vitro (Kroos et al., 1989). The spoIIID83 mutation (by which the locus was originally identified), was sequenced and found to be a single base substitution in the ribosome binding site upstream of the spoIIID open reading frame. A transcriptional fusion to lacZ was constructed and used to examine the regulation of spoIIID. Expression of spoIIID occurred only during sporulation, beginning 1.5 to 2 hours after the initiation of sporulation. The dependence of spoIIID expression on other spo loci suggests that it is mother‐cell‐specific, and that it is transcribed by sigma E‐containing RNA polymerase.