No abstract

During sporulation, Bacillus subtilis undergoes successive morphological changes that can be arrested at various stages by mutations in many genes. One of these, spollGB, encodes a transcriptional factor, cr ~, which is necessary to proceed beyond stage II and to differentiate the cell in two compartments, the forespore and the mother cell. Mutations were introduced in an open reading [tame located immediately downstream of spollGB. They block sporulation at stage III and define a new gene, spolllG, encoding a 260-amino-acid polypeptide highly similar to bacterial ~r-factors. A promoter was identified in the spollGB-spolllG interval by transcriptional fusion to lacZ. It is turned on I hr after the start of ~r ~ synthesis and is specifically activated in the forespore. The tandemly arranged spollGB and spoHIG genes appear to encode homologous proteins that modulate transcription in a sequential fashion during sporulation.

SummarySporulation in Bacillus subtilis is a primitive differentiation process involving two cell types, the forespore and the mother cell. Each cell implements two successive transcription programmes controlled by specific sigma factors. We report that activity of s G , the late forespore sigma factor, is kept in check by Gin, the product of csfB, a gene controlled by s F , the early forespore sigma factor. Gin abolishes s G transcriptional activity when s G is artificially synthesized during growth, but has no effect on s F . Gin interacts strongly with s G but not with s F in a yeast two-hybrid experiment. The absence of Gin allows s G to be active during sporulation independently of the mother-cell development to which it is normally coupled. Premature s G activity leads to the formation of slowgerminating spores, and complete deregulation of s G synthesis is lethal when combined with gin inactivation. Gin allows s F to delay the switch to the late forespore transcription programme by preventing s G to take over before the cell has reached a critical stage of development. A similar strategy, following a completely unrelated route, is used by the mother cell.

Sporulation in Bacillus subtilis is initiated by an asymmetric division generating two cells of different size and fate. During a short interval, the smaller forespore harbors only 30% of the chromosome until the remaining part is translocated across the septum. We demonstrate that moving the gene for F , the forespore-specific transcription factor, in the trapped region of the chromosome is sufficient to produce spores in the absence of the essential activators SpoIIAA and SpoIIE. We propose that transient genetic asymmetry is the device that releases SpoIIE phosphatase activity in the forespore and establishes cell specificity.