The spoIIIA operon of Bacillus subtilis defines a new temporal class of mother‐cell‐specific sporulation genes under the control of the σ^E form of RNA polymerase

Abstract

We have cloned and characterized a 5 kbp region of the Bacillus subtilis chromosome and show that it contains the promoter-proximal part of the spoIIIA locus. The locus consists of a polycistronic operon containing at least three genes. We show that the operon is regulated at the transcriptional level, from a promoter that is first activated about 80 minutes after the induction of sporulation, immediately after septation. Expression of spoIIIA in different spo mutant backgrounds correlates with the ability of each strain to synthesize the sporulation-specific sigma factor, sigma E. Moreover, synthesis of sigma E in vegetative cells by use of an inducible promoter causes expression of mother-cell-specific genes spoIID, spoIIIA, and spoIIID, but not the prespore-specific genes, spoIIIG and spoVA. We suggest that sigma E may be the primary determinant of mother-cell-specific gene expression and that the SpoIIID protein exerts an additional level of regulation on spoIIIA, apparently by acting as a transcriptional repressor. Since the onset of spoIIID expression occurs about 10 minutes after that of spoIIIA, spoIIIA expression is transient. Thus spoIIIA defines a third temporal class of gene controlled by the sigma E form of RNA polymerase.

Genome-wide analysis of temporally regulated and compartment-specific gene expression in sporulating cells of Bacillus subtilis

“…A third class includes 20 genes which are maximally induced around 210 min, and whose expression persists at later times in development. spoIID (Rong et al, 1986) and the SpoIIID-repressed spoIIIA operon (Illing & Errington, 1991) are both found in class 1. Expression of the spoIIIA operon occurs transiently, prior to the accumulation of SpoIIID to high cellular levels (Illing & Errington, 1991), which fits well with the overall pattern of class 1 genes, and suggests that other genes in this class may be subjected to repression.…”

“…spoIID (Rong et al, 1986) and the SpoIIID-repressed spoIIIA operon (Illing & Errington, 1991) are both found in class 1. Expression of the spoIIIA operon occurs transiently, prior to the accumulation of SpoIIID to high cellular levels (Illing & Errington, 1991), which fits well with the overall pattern of class 1 genes, and suggests that other genes in this class may be subjected to repression. In contrast, the spoIIID gene itself and spoIVCB (encoding the N-terminal half of s K ), both of which are known to be SpoIIID dependent Sato et al, 1994;Stevens & Errington, 1990), are found in class 2.…”

“…The distinction between classes 1 and 2 may be attributable mostly to the effects of the regulatory protein SpoIIID upon s E -dependent gene expression (Zheng & Losick, 1990). SpoIIID-independent genes are expressed early, and SpoIIID-dependent genes are expressed later, while the expression of some of the early genes is repressed or switched off Illing & Errington, 1991;Kroos et al, 1989;Kunkel et al, 1989). However, class 3 may represent an overlap between the s E and s K regulons, either because genes in this class have multiple promoters utilized by s E or s K , or because atypical s E -type promoters can also be recognized by s K (Helmann & Moran, 2002 Table S2), encodes a putative transcriptional regulator, highly similar to RsfA.…”

“…Mutations in several s E -governed genes that block the engulfment process at various stages also prevent the activation of s G in the prespore, emphasizing the link between morphogenesis and gene expression (Errington, 2003;Hilbert & Piggot, 2004;Stragier & Losick, 1996). However, the completion of engulfment is not sufficient for the activation of s G , which also requires expression of the spoIIIA octacistronic operon in the mother cell (Illing & Errington, 1991;Kellner et al, 1996;Piggot & Coote, 1976). Hence, signalling of s G activation following the completion of engulfment is an important function of s E .…”

Role of the Anti-Sigma Factor SpoIIAB in Regulation of σ G during Bacillus subtilis Sporulation

“…G accumulates in spoIIIA or spoIIIJ mutant cells but is unable to activate transcription from its target promoters (19,41). The spoIIIA operon encodes several putative membrane proteins and is expressed in the mother cell under the direction of E (15). The spoIIIJ gene is expressed during vegetative growth and encodes a membrane protein translocase of the YidC/Oxap1 family (6,27,48).…”