Establishment of cell‐specific transcription during sporulation in Bacillus subtilis

Abstract

SummaryOne of the most intriguing questions posed by bacterial spore formation concerns the establishment of cell-specific gene expression in the prespore and mother celi. Recent results now suggest that sigma factors, in addition to their temporal roles in the control of gene expression, may aiso be the i<ey determinants of differential gene expression during sporuiation in Baciiius subtiiis. The genes encoding two sporuiatlon-specific sigma factors, a^ and a*", are expressed soon after the initiation of sporuiatlon, before the formation of the spore septum that separates the prespore and mother ceii compartments, it now appears that c^ and a^ direct transcription only after septation and then In a specific ceil type, suggesting that the segregation of the sigma activities after septation is a i<ey event in the establishment of differential gene expression. The mechanism responsible for this segregation is compiex, involving at least seven other gene products. We discuss possible modeis for the interactions between the sigma factors and the establishment of celi-specific transcription.

Evidence that the spoIIM gene of Bacillus subtilis is transcribed by RNA polymerase associated with sigma E

“…In the one case for which direct evidence has been sought through immunoelectron microscopy (spoIID), expression of a gene transcribed by Eo&E was found to be restricted to the mother cell, within the resolution of the technique (14). Thus, it has been previously proposed that the mother cell-specific activation of o&E is in part responsible for the establishment of separate programs of gene expression in the two sporangium compartments (16,41,44). The results of experiments in which we determined 13-galactosidase activity in subcellular fractions prepared from strains containing spoIIM-lacZ fusions do support the conclusion that most expression of spoIIM occurs in the mother cell (Table 3).…”

“…Several genes known to be transcribed by &rE-associated RNA polymerase are expressed exclusively in the mother cell compartment, which has led to the suggestion that &-E activity may be restricted to that compartment (14)(15)(16)41). If so, and if spolIM is expressed exclusively by &--associated RNA polymerase, then expression of spofIM in the forespore compartment should not be required for sporulation.…”

“…At some point very soon after asymmetric septation, the mother cell and the forespore compartments begin to execute quite distinct programs of gene expression. The mechanisms responsible for establishing these compartment-specific programs are not fully understood, but they apparently involve, in part, the compartment-specific activation of RNA polymerase sigma factors (16,40,41,76). This is most obvious at the later stages of sporulation, in which a polymerase species associated with g is active exclusively in the mother cell compartment (11,36,43) and a species associated with cyG is active exclusively in the forespore (31, 78).…”

From spores to antibiotics via the cell cycle

“…The other proteins in the loci turned out to encode regulatory proteins that control the activity of their respective s factor. We realized that s F and s E , which became active at about the same early time point in sporulation, were active in different compartments -s F in the prespore and s E in the mother cell (Errington & Illing, 1992). This realization provided the basis for understanding cell fate determination.…”

Activity of mutant sigma F proteins truncated near the C terminus

“…Early in development, an asymmetric septum divides the sporulating cell into two compartments, the forespore and the mother cell, in which gene expression occurs differentially (15). As sporulation proceeds, the cells manufacture a succession of sigma factors, each of which directs the RNA polymerase to transcribe certain sporulation-specific genes (6,19,31). Because these sigma factors are not needed for growth, they can be altered without affecting the viability of the cell; they are therefore ideally suited to studies of structure and function.…”