Timing of spoII gene expression relative to septum formation during sporulation of Bacillus subtilis

Abstract

spoII mutants formed heat-resistant spores when transformed with spo+ DNA near the start of sporulation. Many of the spores formed remained genetically spoIl. It is deduced from this result and previous epistasis experiments that the spoIl loci are transcribed before the spore septum is formed.Formation of the asymmetrically sited sporulation septum is a crucial event in spore formation. A series of genetic loci, the spoIlI loci, are defined by mutations that permit formation of the spore septum but prevent any further morphological development (11). These loci are clearly essential for spore formation, but their exact relation to formation of the septum is unclear; in all cases the appearance of a spoII mutant septum is different from that of the wild-type sporulation septum. Two spoII loci, spoIIA and spoIIG, include genes coding for RNA polymerase sigma factors (9). CE, the product of spoIIGB (a gene within the spoIIG locus), is first made as an inactive precursor, P31 (7). Appearance of P31 coincides with transcription of spoIIG; processing of P31 to uE begins about 1 h after P31 formation (7). Processing depends on the activity of spoIIGA (the first gene of the spoIlIG locus) and of the polycistronic spoIIA and spoIIE loci (7, 13). It has been proposed that the processing of p31 by the product of spoIIGA is triggered by correct formation of the spore septum (7, 13); spolIA and spoIlE are presumed to be required for correct septum formation and hence for processing (13). A major attraction of this hypothesis is that it ties the complex pattern of gene transcription during spore formation to a critical morphological event. Determination of the time of transcription of spoIIA, spoIIE, and spoIIG relative to the formation of the septum would clearly provide a test for the hypothesis.The two cells that result from correct sporulation septum formation are of unequal size, and their developmental fates are radically different: the forespore becomes the heatresistant spore, whereas the mother cell ultimately lyses. Both cells are necessary for spore formation. We had previously devised a genetic method to demonstrate compartmentalization of late spo locus expression during sporulation (8). The method utilized the following facts: shortly before spore septum formation, two copies of the chromosome are present in one cell; and one chromosome is destined for the mother cell, and the other is destined for the forespore. By transforming spo mutants as they started to sporulate, it was possible to obtain conditions in which only one of the two copies of the chromosome was likely to have been transformed with the spo+ marker. (Bacteria that are already sporulating are refractory to transformation.) The spo+ chromosome could presumably end up in the mother cell or in the forespore. If correct expression in the mother cell is sufficient for spore formation, then it should be possible to obtain heat-resistant spores that are genetically asporogenous (spo). However, if transcription in the fore-* Corresponding author. spore i...

Compartmentalized distribution of the proteins controlling the prespore‐specific transcription factor σF of Bacillus subtilis

“…In the t 1:5 sample, more than half of the cells with detectable j F (39% of total cells) were at the preseptation stage (Table 1). This was in accordance with previous direct and indirect experiments showing that induction of the spoIIA operon, encoding j F , occurs before septation (Gholamhoseinian & Piggot 1989;Partridge & Errington 1993;Bylund et al 1994). From t 1.5 to t 3 the proportion of pre-septational cells containing j F decreased, and the number of postseptational cells increased concomitantly.…”

Compartmentalization of Gene Expression duringBacillus subtilisSpore Formation

“…However, shortly thereafter, it became clear that the third gene in the operon, spoIIAC, encoded a product that was homologous to an RNA polymerase factor (62,274), named F (183). The first targets identified for E-F action were spoIIIG and gpr (282,285), and the site of expression of spoIIIG was shown to be the prespore (93,142,189), as it has been for all E-F -directed genes analyzed subsequently (231).…”

“…Although the spoIIA operon is expressed prior to asymmetric division (93,218), F does not become active until after asymmetric division (93,142). It seemed likely that F was subject to some form of posttranslational regulation, and genetic analysis revealed that the other two products of the spoIIA operon, SpoIIAA and SpoIIAB, regulate its activity.…”

Septation, dephosphorylation, and the activation of sigma F during sporulation in Bacillus subtilis

“…The F factor is synthesized shortly after the onset of sporulation in the predivisional sporangium (Gholamhoseinian and Piggot 1989). It does not become active in directing gene transcription, however, until after asymmetric division, when its activity is confined to the forespore (Margolis et al 1991).…”