Identification of the transcriptional suppressor sof-1 as an alteration in the spo0A protein

The mutation sof-1 suppresses the sporulation defect of mutations in either the spo0B, spo0E, or spo0F stage 0 sporulation genes. Through the use of integrative plasmids carrying the portion of the chromosome including the spo0A locus and flanking regions, the sof-1 mutation was localized near the spo0A locus. A plasmid carrying a fragment of DNA with sof genetic activity was constructed. Nucleic acid sequence analysis of this fragment revealed a single base change that resulted in a substitution of lysine for asparagine in the 12th codon of the spo0A gene. The results indicate that certain missense mutations in the spo0A gene bypass the necessity for the spo0B, spo0E, and spo0F gene products in sporulation. Several models for the interaction of these gene products may be imagined.     

Temporal regulation of the Bacillus subtilis early sporulation gene spo0F

The initiation of sporulation in Bacillus subtilis depends on seven genes of the spo0 class. One of these, spo0F, codes for a protein of 14,000 daltons. We studied the regulation of spo0F by using spo0F-lacZ translational fusions and also measured Spo0F protein levels by immunoassays. spo0F-lacZ and Spo0F levels increased as the cells entered the stationary phase, and this effect was repressed by glucose and glutamine. Decoyinine, which lowers GTP levels and allows sporulation in the presence of normally repressing levels of glucose, induced spo0F-lacZ expression and raised Spo0F levels. The expression of spo0F-lacZ was dependent on spo0A, -0B, -0E, -0F, and -0H genes, a spo0H deletion causing the strongest effect. In most respects, the spo0F gene was regulated in a manner similar to that of spoVG. However, the presence of an abrB mutation did not relieve the dependence of spo0F gene expression on spo0A, as it does with spoVG (P. Zuber and R. Losick, J. Bacteriol. 169:2223-2230, 1987).     

New suppressor mutation sur0B of spo0B and spo0F mutations in Bacillus subtilis

Two extragenic suppressor mutations, sur0B20 and sur0F1, which restore the sporulation of spo0B or spo0F mutants of Bacillus subtilis to the wild-type level, were obtained. These suppressor mutations were located in the spo0A gene. Their location is close to that of the sof-1 mutation, which suppresses spo0B, spo0E and spo0F mutations. However, spo0 strains bearing the sur0B20 mutation differed in several phenotypic characteristics from spo0 mutants bearing the sof-1 suppressor. Nucleotide sequence analysis revealed that the sur0B20 and sur0F1 mutations resulted in Glu14 to Val and Asn12 to Lys conversion, respectively, in the spo0A gene. This result indicates that sur0B20 is a new suppressor of spo0b and spo0F mutations, whereas sur0F1 is identical to sof-1.     

The effect of spo0 mutations on the expression of spo0A- and spo0F-lacZ fusions

Summary We have constructedspo0A-lacZ andspo0F-lacZ fusions with a temperate phage vector and have investigated howspo0 gene products are involved in the expression of each of these genes. The expression ofspo0A-lacZ andspo0F-lacZ was stimulated at about the time of cessation of vegetative growth in Spo⁺ cells. This stimulation ofspo0A-lacZ was impaired by mutations in thespo0B, D, E, F orH genes but was not affected by mutations in thespo0J orK genes. Similar results were obtained with thespo0F-lacZ fusion. The effect of thespo0A mutation onspo0A-lacZ expression was characteristic: thespo0A-directed β-galactosidase activity found during vegetative growth was significantly enhanced in thespo0A mutant. This result suggests thatspo0A gene expression is autoregulated being repressed by its own gene product. Another remarkable observation was the effect of thesof-1 mutation, which is known to be aspo0A allele; it suppressed the sporulation deficiency ofspo0B, spo0D andspo0F mutants. Thespo0A-lacZ stimulation, which is impaired by any one of thesespo0 mutations, was restored by the additionalsof-1 mutation.     

The Bacillus subtilis SinR protein is a repressor of the key sporulation gene spo0A.

SinR is a pleiotropic DNA binding protein that is essential for the late-growth processes of competence and motility in Bacillus subtilis and is also a repressor of others, e.g., sporulation and subtilisin synthesis. In this report, we show that SinR, in addition to being an inhibitor of sporulation stage II gene expression, is a repressor of the key early sporulation gene spo0A. The sporulation-specific rise in spo0A expression at time zero is absent in a SinR-overproducing strain and is much higher than normal in strains with a disrupted sinR gene. This effect is direct, since SinR binds specifically to spo0A in vitro, in a region overlapping the -10 region of the sporulation-specific Ps promoter that is recognized by E-sigma H polymerase. Methyl interference and site-directed mutagenesis studies have identified guanine residues that are important for SinR recognition of this DNA sequence. Finally, we present evidence that SinR controls sporulation through several independent genes, i.e., sp0A, spoIIA, and possibly spoIIG and spoIIE.     

Analysis of the inhibition of sporulation of Bacillus subtilis caused by increasing the number of copies of the spo0F gene

The Bacillus subtilis spo0F gene was cloned on a 6.3 kbp Bg/II fragment. The effect on sporulation of amplification of the spo0F region was examined. Sporulation was inhibited to less than 5% of that of the parental strain when as few as four copies of the spo0F region were present. Subclones, constructed in autonomous or integrative vectors, were used to demonstrate that the region responsible for the copy-number-dependent asporogeny corresponded closely with the spo0F structural gene. A possible mechanism for this effect is discussed.     

Identification and characterization of genes controlled by the sporulation-regulatory gene spo0H in Bacillus subtilis.

We describe a general strategy for the identification of genes that are controlled by a specific regulatory factor in vivo and the use of this strategy to identify genes in Bacillus subtilis that are controlled by spo0H, a regulatory gene required for the initiation of sporulation. The general strategy makes use of a cloned regulatory gene fused to an inducible promoter to control expression of the regulatory gene and random gene fusions to a reporter gene to monitor expression in the presence and absence of the regulatory gene product. spo0H encodes a sigma factor of RNA polymerase, sigma H, and is required for the extensive reprograming of gene expression during the transition from growth to stationary phase and during the initiation of sporulation. We identified 18 genes that are controlled by sigma H (csh genes) in vivo by monitoring expression of random gene fusions to lacZ, made by insertion mutagenesis with the transposon Tn917lac, in the presence and absence of sigma H. These genes had lower levels of expression in the absence of sigma H than in the presence of sigma H. Patterns of expression of the csh genes during growth and sporulation in wild-type and spo0H mutant cells indicated that other regulatory factors are probably involved in controlling expression of some of these genes. Three of the csh::Tn917lac insertion mutations caused noticeable phenotypes. One caused a defect in vegetative growth, but only in combination with a spo0H mutation. Two others caused a partial defect in sporulation. One of these also caused a defect in the development of genetic competence. Detailed characterization of some of the csh genes and their regulatory regions should help define the role of spo0H in the regulation of gene expression during the transition from growth to stationary phase and during the initiation of sporulation.