No abstract

Gene expression in members of the family Bacillaceae becomes compartmentalized after the distinctive, asymmetrically located sporulation division. It involves complete compartmentalization of the activities of sporulation-specific sigma factors, σF in the prespore and then σE in the mother cell, and then later, following engulfment, σG in the prespore and then σK in the mother cell. The coupling of the activation of σF to septation and σG to engulfment is clear; the mechanisms are not. The σ factors provide the bare framework of compartment-specific gene expression. Within each σ regulon are several temporal classes of genes, and for key regulators, timing is critical. There are also complex intercompartmental regulatory signals. The determinants for σF regulation are assembled before septation, but activation follows septation. Reversal of the anti-σF activity of SpoIIAB is critical. Only the origin-proximal 30% of a chromosome is present in the prespore when first formed; it takes ≈15 min for the rest to be transferred. This transient genetic asymmetry is important for prespore-specific σF activation. Activation of σE requires σF activity and occurs by cleavage of a prosequence. It must occur rapidly to prevent the formation of a second septum. σG is formed only in the prespore. SpoIIAB can block σG activity, but SpoIIAB control does not explain why σG is activated only after engulfment. There is mother cell-specific excision of an insertion element in sigK and σE-directed transcription of sigK, which encodes pro-σK. Activation requires removal of the prosequence following a σG-directed signal from the prespore

95 cysA14 60 ery-1 25 purA 49 metC3; 21 ura-1 c 42 ura-26 s 83 ura-1; 5 metC3 ' 54 lys-l' 44 trpC2 35 trpC2 33 Iys-1; 16 trpC2 56 lys-1 25 phe-1; 10 ilvCl RI = 0.1 12 hisAI RI s 0.2 47 ura-1; 1 metC3 12 ura-26 16 ura-1; 49 metC3 49 52 148 307 24 phe-12; 1 lys-l 49 B 49 49, 143, 334 49 244 49 a Linkage with vegetative markers is expressed as % cotransfer. Linkage between spo mutations is expressed as the recombination index (RI [170]). b A, J.A. Hoch, personal communication; B, M. Young, personal communication; C, P.J. Piggot, unpublished observations. I Assignment to locus is not certain, see text. d If 94U (reference 148) is the same as 94 (reference 257), then this has the same phenotype as spoIVC mutants described by Coote (49, 50), and the mutations should be placed in the spoIVC locus.

SummaryThe Escherichia coli rodA and ftsW genes and the spoVE gene of Bacillus subtilis encode membrane proteins that control peptidoglycan synthesis during cellular elongation, division and sporulation respectively. While rodA and ftsW are essential genes in E. coli, the B. subtilis spoVE gene is dispensable for growth and is only required for the synthesis of the spore cortex peptidoglycan. In this work, we report on the characterization of a B. subtilis gene, designated rodA, encoding a homologue of E. coli RodA. We found that the growth of a B. subtilis strain carrying a fusion of rodA to the IPTG-inducible P spac promoter is inducer dependent. Limiting concentrations of inducer caused the formation of spherical cells, which eventually lysed. An increase in the level of IPTG induced a sphere-to-short rod transition that re-established viability. Higher levels of inducer restored normal cell length. Staining of the septal or polar cap peptidoglycan by a fluorescent lectin was unaffected during growth of the mutant under restrictive conditions. Our results suggest that rodA functions in maintaining the rod shape of the cell and that this function is essential for viability. In addition, RodA has an irreplaceable role in the extension of the lateral walls of the cell. Electron microscopy observations support these conclusions. The ultrastructural analysis further suggests that the growth arrest that accompanies loss of the rod shape is caused by the cell's inability to construct a division septum capable of spanning the enlarged cell. RodA is similar over its entire length to members of a large protein family (SEDS, for shape, elongation, division and sporulation). Members of the SEDS family are probably present in all eubacteria that synthesize peptidoglycan as part of their cell envelope.

Sporulation of Bacillus subtilis involves an asymmetric cell division that gives rise to two different types of cells-the larger mother cell, which is required for the formation of the spore but lyses upon its completion, and the smaller forespore cell, destined to become the spore. The fates of the two cells are controlled by separate genetic programs. However, these programs are not independent. Rather, a cascade of crossregulatory events exists to coordinate the programs (1). This cascade starts with the oc factors that initiate the two programs, oE in the mother cell and 0F in the forespore. aE is encoded by the second gene in the spoIIG operon, spoIIGB, as a pro-protein that is activated by the cleavage of 27-29 residues from its NH2-terminal end (1). This cleavage requires the product of the first gene in the operon, spoIIGA.