Catabolite-resistant sporulation (crsA) mutations in the Bacillus subtilis RNA polymerase sigma 43 gene (rpoD) can suppress and be suppressed by mutations in spo0 genes

Role of altered rpoB alleles in Bacillus subtilis sporulation and spore resistance to heat, hydrogen peroxide, formaldehyde, and glutaraldehyde

Mutations in the RNA polymerase β-subunit gene rpoB causing resistance to rifampicin (Rif(R)) in Bacillus subtilis were previously shown to lead to alterations in the expression of a number of global phenotypes known to be under transcriptional control. To better understand the influence of rpoB mutations on sporulation and spore resistance to heat and chemicals, cells and spores of the wild-type and twelve distinct congenic Rif(R) mutant strains of B. subtilis were tested. Different levels of glucose catabolite repression during sporulation and spore resistance to heat and chemicals were observed in the Rif(R) mutants, indicating the important role played by the RNA polymerase β-subunit, not only in the catalytic aspect of transcription, but also in the initiation of sporulation and in the spore resistance properties of B. subtilis.

The threshold level of the sensor histidine kinase KinA governs entry into sporulation in Bacillus subtilis

Sporulation in Bacillus subtilis is controlled by a complex gene regulatory circuit that is activated upon nutrient deprivation. The initial process is directed by the phosphorelay, involving the major sporulation histidine kinase (KinA) and two additional phosphotransferases (Spo0F and Spo0B), that activates the master transcription factor Spo0A. Little is known about the initial event and mechanisms that trigger sporulation. Using a strain in which the synthesis of KinA is under the control of an IPTG (isopropyl-beta-d-thiogalactopyranoside)-inducible promoter, here we demonstrate that inducing the synthesis of the KinA beyond a certain level leads to the entry of the irreversible process of sporulation irrespective of nutrient availability. Moreover, the engineered cells expressing KinA under a sigma(H)-dependent promoter that is similar to but stronger than the endogenous kinA promoter induce sporulation during growth. These cells, which we designated COS (constitutive sporulation) cells, exhibit the morphology and properties of sporulating cells and express sporulation marker genes under nutrient-rich conditions. Thus, we created an engineered strain displaying two cell cycles (growth and sporulation) integrated into one cycle irrespective of culture conditions, while in the wild type, the appropriate cell fate decision is made depending on nutrient availability. These results suggest that the threshold level of the major sporulation kinase acts as a molecular switch to determine cell fate and may rule out the possibility that the activity of KinA is regulated in response to the unknown signal(s).

A viable Bacillus subtilis strain without functional extracytoplasmic function sigma genes

We constructed a Bacillus subtilis Marburg strain that harbors deletion mutations in all seven extracytoplasmic function (ECF) sigma genes. The strain shows wild-type growth at 37 degrees C both in a complex and in a synthetic medium and exhibits wild-type sporulation. ECF sigma genes of B. subtilis are dispensable as long as no stress is imposed, although they seem to be required for quick response to stresses.

Involvement of the YneS/YgiH and PlsX proteins in phospholipid biosynthesis in both Bacillus subtilis and Escherichia coli

Background

Phospholipid biosynthesis commences with the acylation of glycerol-3-phosphate (G3P) to form 1-acyl-G3P. This step is catalyzed by the PlsB protein in Escherichia coli. The gene encoding this protein has not been identified, however, in the majority of bacterial genome sequences, including that of Bacillus subtilis. Recently, a new two-step pathway catalyzed by PlsX and PlsY proteins for the initiation of phospholipid formation in Streptococcus pneumoniae has been reported.

Results

In B. subtilis, 271 genes have been reported to be indispensable, when inactivated singly, for growth in LB medium. Among these, 11 genes encode proteins with unknown functions. As part of a genetic study to identify the functions of these genes, we show here that the B. subtilis ortholog of S. pneumoniae PlsY, YneS, is required for G3P acyltransferase activity, together with PlsX. The B. subtilis genome lacks plsB, and we show in vivo that the PlsX/Y pathway is indeed essential for the growth of bacteria lacking plsB. Interestingly, in addition to plsB, E. coli possesses plsX and the plsY ortholog, ygiH. We therefore explored the functional relationship between PlsB, PlsX and YgiH in E. coli, and found that plsB is essential for E. coli growth, indicating that PlsB plays an important role in 1-acyl-G3P synthesis in E. coli. We also found, however, that the simultaneous inactivation of plsX and ygiH was impossible, revealing important roles for PlsX and YgiH in E. coli growth.

Conclusion

Both plsX and yneS are essential for 1-acyl-G3P synthesis in B. subtilis, in agreement with recent reports on their biochemical functions. In E. coli, PlsB plays a principal role in 1-acyl-G3P synthesis and is also essential for bacterial growth. PlsX and YgiH also, however, play important roles in E. coli growth, possibly by regulating the intracellular concentration of acyl-ACP. These proteins are therefore important targets for development of new antibacterial agents.

Evidence that Bacillus catabolite control protein CcpA interacts with RNA polymerase to inhibit transcription

Summary Bacilluscatabolite control protein (CcpA) mediates carbon catabolite repression (CCR) by controlling expression of catabolite responsive (CR) genes or operons through interaction with catabolite responsive elements (cres) located within or outside of CR promoters. Here, we investigated how CcpA inhibits the transcription of CR promoters in vitro. CcpA has different affinities for different cres, but this does not correlate with its ability to inhibit transcription. In the amyE promoter, which overlaps a CcpA binding site (amyE cre centred at +4.5), CcpA does not prevent RNA polymerase (RNAP) binding to the promoter; it may even interact with RNAP. Inserting non-integral turns of helix (1.5 and 2.5) between the amyE promoter (-10 hexamer) and the amyE cre relieved CCR of amyE expression. In the xyl operon, despite the downstream location of its cre (a major cre centred at +130.5), CcpA blocked transcription initiation, not elongation (roadblock) at the site of the cre. Taken together, our results strongly suggest that CcpA requires interactions with RNAP to inhibit transcription.

Glucose-resistant sporulation in Bacillus subtilis crsA47 mutants does not depend on promoter switching at the spo0A gene

We have found that sporulation in Bacillus subtilis crsA47 mutants does not require the sigma(H)-dependent promoter of the spo0A gene. This implies that the glucose-resistant sporulation phenotype of this strain is not related to the switch from the vegetative-stage sigma(A)-dependent promoter to the sigma(H)-dependent promoter at the spo0A gene.

Developmental gene expression in Bacillus subtilis crsA47 mutants reveals glucose-activated control of the gene for the minor sigma factor sigma(H)

The presence of excess glucose in growth media prevents normal sporulation of Bacillus subtilis. The crsA47 mutation, located in the gene for the vegetative phase sigma factor (sigma(A)) results in a glucose-resistant sporulation phenotype. As part of a study of the mechanisms whereby the mutation in sigma(A) overcomes glucose repression of sporulation, we examined the expression of genes involved in sporulation initiation in the crsA47 background. The crsA47 mutation had a significant impact on a variety of genes. Changes to stage II gene expression could be linked to alterations in the expression of the sinI and sinR genes. In addition, there was a dramatic increase in the expression of genes dependent on the minor sigma factor sigma(H). This latter change was paralleled by the pattern of spo0H gene transcription in cells with the crsA47 mutation. In vitro analysis of RNA polymerase containing sigma(A47) indicated that it did not have unusually high affinity for the spo0H gene promoter. The in vivo pattern of spo0H expression is not predicted by the known regulatory constraints on spo0H and suggests novel regulation mechanisms that are revealed in the crsA47 background.

Suppression of temperature-sensitive sporulation mutation in the Bacillus subtilis sigA gene by rpoB mutation

We isolated a temperature-sensitive sporulation defective mutant of the sigA gene, encoding a major sigma factor, sigma(A) protein, in Bacillus subtilis, and designated it as sigA21. The sigA21 mutation caused a single-amino acid substitution, E314K, in region 4 of the sigma(A) protein. In this mutant, expression of the spoIIG gene, whose transcription depends on both sigma(A) and the phosphorylated Spo0A protein, Spo0A approximately P, a major transcription factor during early stages of sporulation, was greatly reduced at 43 degrees C. To obtain further information on the mechanism of sigma(A) function during the early spore development, we isolated a spontaneous sporulation-proficient suppressor mutant at 43 degrees C. This extragenic suppressor mutation was mapped within the rpoB gene, encoding the beta subunit of RNA polymerase, and was found to have a single-amino acid substitution, A863G. In this mutant, the expression of the spoIIG is partially restored at 43 degrees C.

Analysis of tnrA alleles which result in a glucose-resistant sporulation phenotype in Bacillus subtilis

Bacillus subtilis cells cannot sporulate in the presence of catabolites such as glucose. During the analysis of Tn10-generated mutants, we found that deletion of the C-terminal region of the tnrA gene, which encodes a global regulator that positively regulates a number of genes in response to nitrogen limitation, results in a catabolite-resistant sporulation phenotype. Analyses of nrg-lacZ and nasB-lacZ, which are activated by TnrA under nitrogen limitation, showed that C-terminally truncated TnrA activates nitrogen-regulated genes constitutively. The relief of catabolite repression of sporulation may result from the uncontrolled expression of the TnrA-regulated genes.

Analysis of an insertional operator mutation (gntOi) that affects the expression level of the Bacillus subtilis gnt operon, and characterization of gntOi suppressor mutations

The Bacillus subtilis gnt operon is negatively regulated via interaction of the gnt repressor (GntR) with an operator upstream of gntR, which is antagonized by gluconate. An 8 bp insertional operator mutation (gntOi) of the gnt operon was constructed which affected the expression level of this operon. Two suppressors of this gntOi mutation, exhibiting normal expression, were also isolated; one involved a threonine substitution for the Ala-48 residue (gntR48T) within the helix-turn-helix DNA-binding motif of GntR, and the other an adenine substitution for the guanine at nucleotide -4 within the gntOi operator (gntOiM4A) (+ 1 is the transcription initiation site). The gntR48T mutation by itself rendered the gnt operon partially constitutive. When the gntR43L mutation, which renders the gnt operon fully constitutive, was introduced into the gntOi or gntOiM4A mutant, the operator mutations were found not to affect the promoter activity of the gnt operon. These in vivo results indicate that the gntOi mutation affects the operator interaction with GntR, causing a low expression level even in the presence of gluconate. In vitro gel retardation and DNase I footprint analyses demonstrated that even when gluconate was present, GntR still bound to the gntOi operator region.

Krebs cycle function is required for activation of the Spo0A transcription factor in Bacillus subtilis

Expression of genes early during sporulation in Bacillus subtilis requires the activity of the transcription factor encoded by spo0A. The active, phosphorylated form of Spo0A is produced through the action of a multicomponent pathway, the phosphorelay. A mutant defective in the first three enzymes of the Krebs citric acid cycle was unable to express early sporulation genes, apparently because of a failure to activate the phosphorelay. Cells that produce an altered Spo0A protein that can be phosphorylated by an alternative pathway were not dependent on Krebs cycle function for early sporulation gene expression. These findings suggest that Krebs cycle enzymes transmit a signal to activate the phosphorelay and that B. subtilis monitors its metabolic potential before committing itself to spore formation.

The sigma factors of Bacillus subtilis

The specificity of DNA-dependent RNA polymerase for target promotes is largely due to the replaceable sigma subunit that it carries. Multiple sigma proteins, each conferring a unique promoter preference on RNA polymerase, are likely to be present in all bacteria; however, their abundance and diversity have been best characterized in Bacillus subtilis, the bacterium in which multiple sigma factors were first discovered. The 10 sigma factors thus far identified in B. subtilis directly contribute to the bacterium's ability to control gene expression. These proteins are not merely necessary for the expression of those operons whose promoters they recognize; in many instances, their appearance within the cell is sufficient to activate these operons. This review describes the discovery of each of the known B. subtilis sigma factors, their characteristics, the regulons they direct, and the complex restrictions placed on their synthesis and activities. These controls include the anticipated transcriptional regulation that modulates the expression of the sigma factor structural genes but, in the case of several of the B. subtilis sigma factors, go beyond this, adding novel posttranslational restraints on sigma factor activity. Two of the sigma factors (sigma E and sigma K) are, for example, synthesized as inactive precursor proteins. Their activities are kept in check by "pro-protein" sequences which are cleaved from the precursor molecules in response to intercellular cues. Other sigma factors (sigma B, sigma F, and sigma G) are inhibited by "anti-sigma factor" proteins that sequester them into complexes which block their ability to form RNA polymerase holoenzymes. The anti-sigma factors are, in turn, opposed by additional proteins which participate in the sigma factors' release. The devices used to control sigma factor activity in B, subtilis may prove to be as widespread as multiple sigma factors themselves, providing ways of coupling sigma factor activation to environmental or physiological signals that cannot be readily joined to other regulatory mechanisms.

The response of a Bacillus subtilis temperature-sensitive sigA mutant to heat stress

The mutant sigA allele of Bacillus subtilis DB1005 was confirmed to be temperature sensitive (ts) and transferable among strains of B. subtilis by chromosomal transformation and gene conversion. This ts sigA allele had a pleiotropic effect on gene expression of DB1005. The induction of certain heat shock proteins in DB1005 was markedly less significant than that observed in the wild-type strain (DB2) under heat stress. In contrast, some proteins required for coping with oxidative stress and glucose starvation were induced abruptly in DB1005 but not in DB2. Heat induction of the groEL gene in vivo at both transcription and translation levels was much lower in DB1005 than in DB2. Besides, the putative sigma A-type promoter from the groESL operon of B. subtilis was able to be transcribed by the reconstituted sigma A RNA polymerase in vitro at both 37 and 49 degrees C. These results strongly suggest that the expression of the groEL gene of B. subtilis under heat stress is regulated at least in part by sigma A at the level of transcription. Our results also showed that DB1005 did not respond too differently from the wild type to ethanol stress, except after a relatively long exposure.

Mutations in pts cause catabolite-resistant sporulation and altered regulation of spo0H in Bacillus subtilis

A mutation in Bacillus subtilis, ggr-31, that relieves glucose-glutamine-dependent control of a spoVG-lacZ translational fusion was isolated and was subsequently found to confer a pleiotropic phenotype. Mutants cultured in glucose- and glutamine-rich media exhibited a Crs- (catabolite-resistant sporulation) phenotype; enhanced expression of the spo0H gene, encoding sigma H, as evidenced by immunoblot analysis with anti-sigma H antiserum; and derepression of srfA, an operon involved in surfactin biosynthesis and competence development. In addition, ggr-31 mutants exhibited a significant increase in generation time when they were cultured in minimal glucose medium. The mutant phenotype was restored to the wild type by Campbell integration of a plasmid containing part of the ptsG (encoding the enzyme II/III glucose permease) gene, indicating that the mutation probably resides within ptsG and adversely affects glucose uptake. A deletion mutation within ptsI exhibited a phenotype similar to that of ggr-31.

Catabolite repression of the Bacillus subtilis gnt operon mediated by the CcpA protein

Inducer exclusion was not important in catabolite repression of the Bacillus subtilis gnt operon. The CcpA protein (also known as AlsA) was found to be necessary for catabolite repression of the gnt operon, and a mutation (crsA47, which is an allele of the sigA gene) partially affected this catabolite repression.

Temperature-sensitive sporulation caused by a mutation in the Bacillus subtilis secY gene

A thermosensitive sporulation mutant of Bacillus subtilis containing a mutation in the secY gene was isolated and characterized. No asymmetric septum specific to the sporulation was detected by electron microscopy at the nonpermissive temperature, indicating that the block occurred at a very early stage of sporulation. Furthermore, competence development in the mutant cell was affected even at the sporulation-proficient temperature. It is assumed that the SecY protein of B. subtilis has multiple roles both in the regulation of spore formation and in stationary-phase-associated phenomena.

Roles of rpoD, spoIIF, spoIIJ, spoIIN, and sin in regulation of Bacillus subtilis stage II sporulation-specific transcription

Bacillus subtilis strains containing defects in the sporulation gene spoIIF (kinA), spoIIJ (kinA), or spoIIN (ftsA) cannot transcribe the sigma E-dependent gene spoIID. Results presented here and by other workers demonstrate that the spoIIF, spoIIJ, and spoIIN gene products control spoIID transcription indirectly by coordinating the induction of the spoIIGAB, spoIIE, and spoIIAC operons, which are required for sigma E synthesis and processing. Sporulation competence and spoIIGAB, spoIIE, and spoIIAC transcription were restored in spoIIF, spoIIJ, and spoIIN mutants by introduction of crsA47, a mutation in the major vegetative sigma factor sigma A. crsA mutations are known to restore sporulation in certain spo0 mutants. crsA suppression of kinA and ftsA mutations was achieved through inhibition of the transcription of sin, a gene involved in the selection between several post-exponential-phase cell states. A deletion of sin restored sporulation competence in spoIIF, spoIIJ, or spoIIN mutant strains. A sin deletion was also able to restore sporulation competence in the crsA suppressible stage 0 mutant spo0K141.

Localization of a new promoter, P5, in the sigA operon of Bacillus subtilis and its regulation in some spo mutant strains

The sigA operon of Bacillus subtilis is transcribed from at least two SigA and two SigH promoters. Primer extension and promoter probe analyses have localized a fifth promoter, P5, that is active only at later sporulation stages (T3 to T5). Mutations in the genes for the sigma factors SigG, SigK, SigH, and SigE do not block transcription from P5. The expression from P5 is blocked or severely reduced in spo0A, spo0B, spo0E, and spo0K mutants.

Differential regulation of spo0A transcription in Bacillus subtilis: glucose represses promoter switching at the initiation of sporulation

We have shown by S1 nuclease mapping with in vivo transcripts that the differential expression of a sporulation-regulatory gene, spo0A, is regulated by switching of two discrete promoters during the initiation of sporulation in Bacillus subtilis; vegetative mRNA was transcribed from an upstream promoter (Pv, vegetative promoter), and sporulation-specific mRNA was transcribed from the other promoter (Ps, sporulation-specific promoter) about 150 bp downstream of the Pv promoter. Transcription from the Pv promoter was at a low level and shut off at T0.5. On the other hand, transcription from the Ps promoter was strongly induced at T0.5 and increased until T2.5. In the presence of 2% glucose, Pv-directed transcription was not shut off and was observed even at T1.5, whereas the induction of Ps-directed transcription was completely repressed. A mutant in which the spo0A gene was transcribed only from the Ps promoter could sporulate normally in the presence of 0.1% glucose but could not sporulate at all in the presence of 2% glucose. In a catabolite-resistant sporulation mutant carrying crsA47 (sigA47), a mutation within the gene encoding sigma A, normal promoter switching from Pv to Ps was observed in the presence of 2% glucose.

The Bacillus subtilis spo0J gene: evidence for involvement in catabolite repression of sporulation

Previous observations concerning the ability of the Bacillus subtilis bacteriophages SP10 and PMB12 to suppress mutations in spo0J and to make wild-type sporulation catabolite resistant suggested that spo0J had a role in catabolite repression of sporulation. This suggestion was supported in the present report by the ability of the catabolite-resistant sporulation mutation crsF4 to suppress a Tn917 insertion mutation of the B. subtilis spo0J locus (spo0J::Tn917 omega HU261) in medium without glucose. Although crsF4 and SP10 made wild-type B. subtilis sporulation catabolite resistant, neither crsF4 nor SP10 caused a mutant with spo0J::Tn917 omega HU261 to sporulate in medium with glucose. Sequencing the spo0J locus revealed an open reading frame that was 179 codons in length. Disruption of the open reading frame resulted in a sporulation-negative (Spo-) phenotype that was similar to those of other spo0J mutations. Analysis of the deduced amino acid sequence of the spo0J locus indicated that the spo0J gene product contains an alpha-helix-turn-alpha-helix unit similar to the motif found in lambda Cro-like DNA-binding proteins.

Novel mutations that alter the regulation of sporulation in Bacillus subtilis. Evidence that phosphorylation of regulatory protein SpoOA controls the initiation of sporulation

Sporulation in Bacillus subtilis is a complex developmental process that occurs in response to nutrient deprivation. To identify components of the mechanism that allows cells to monitor their nutritional status and to understand how this sensory information is transduced into a signal to activate specific sporulation genes, we have isolated mutants that are able to sporulate efficiently under nutritional conditions that strongly inhibit sporulation in wild-type bacteria, a phenotype we refer to as Coi (control of initiation). Four coi mutations were found to be within the coding sequence of spoOA, a gene in which null mutations prevent the initiation of sporulation and a gene whose product shares a domain of homology with phosphorylation-activated proteins that play signal transduction roles in bacteria. All four of the spoOA mutations were within this conserved domain and in close proximity to the presumptive phosphoacceptor site. The wild-type and one of the mutant SpoOA proteins were purified and shown to be competent to accept phosphoryl groups from a phosphohistidine within a bacterial signal transduction kinase (CheA). The mutant SpoOA protein exhibited enhanced phosphoacceptor activity compared with the wild-type. This property of the mutant protein, together with additional genetic information, supports a model for regulation of sporulation initiation by control of the phosphorylation level of SpoOA.

Complex character of senS, a novel gene regulating expression of extracellular-protein genes of Bacillus subtilis

The senS gene of Bacillus subtilis, which in high copy number stimulates the expression of several extracellular-protein genes, has been cloned, genetically mapped, and sequenced. The gene codes for a highly charged basic protein containing 65 amino acid residues. The gene is characterized by the presence of a transcription terminator (attenuator) located between the promoter and open reading frame, a strong ribosome-binding site, and a strong transcription terminator at the 3' end of this monocistronic gene. The amino acid sequence of SenS showed partial homology with the N-terminal core binding domain region of bacterial RNA polymerase sigma factors and a helix-turn-helix motif found in DNA-binding proteins. The gene can be deleted without any effect on growth or sporulation.

Induction of levansucrase in Bacillus subtilis: an antitermination mechanism negatively controlled by the phosphotransferase system

The target of the induction by sucrose of the levansucrase gene is a transcription terminator (sacRt) located upstream from the coding sequence, sacB. The two-gene locus sacX-sacY (formerly sacS) and the ptsI gene were previously shown to be involved in this induction. ptsI encodes enzyme I of the phosphoenolpyruvate-dependent phosphotransferase system. SacX is strongly homologous to sucrose-specific phosphotransferase system-dependent permeases. SacY is a positive regulator of sacB. Here we show that SacY is probably an antiterminator interacting directly with sacRt, since in Escherichia coli the presence of the sacY gene stimulates the expression of a reporter gene fused downstream from sacRt. Missense mutations affecting sacY were sequenced, and the sacB regulation was studied in isogenic strains carrying these mutations or in vitro-generated mutations affecting sacX, sacY, or ptsI. The phenotype of double mutants suggests a model in which SacX might be a sucrose sensor that would be phosphorylated by the phosphotransferase system and, in this state, could inhibit the SacY antiterminator. Exogenous sucrose, or a mutation inactivating the phosphotransferase system, would dephosphorylate SacX and allow antitermination at sacRt.

cis sequences involved in modulating expression of Bacillus licheniformis amyL in Bacillus subtilis: effect of sporulation mutations and catabolite repression resistance mutations on expression

Nutrient conditions which trigger sporulation also activate expression of the Bacillus licheniformis alpha-amylase gene, amyL. Glucose represses both spore formation and expression of amyL. A fusion was constructed between the B. licheniformis alpha-amylase regulatory and 5' upstream sequences (amyRi) and the Escherichia coli lacZ structural gene to identify sequences involved in mediating temporal activation and catabolite repression of the amyL gene in Bacillus subtilis. amyRi-directed expression in a variety of genetic backgrounds and under different growth conditions was investigated. A 108-base-pair sequence containing an inverted repeat sequence, ribosome-binding site, and 26 codons of the structural gene was sufficient to mediate catabolite repression of amyL. spo0 mutations (spo0A, spo0B, spo0E, and spo0H) had no significant effect on temporal activation of the gene fusion when the recipient strains were grown in nonrepressing medium. However, in glucose-grown cultures the presence of a spo0A mutation resulted in more severe repression of amyRi-lacZ. In contrast, a spo0H mutation reduced the repressive effect of glucose on amyRi-lacZ expression. The spo0A effect was relieved by an abrB mutation. Initiation of sporulation is not a prerequisite for either temporal activation or derepression of alpha-amylase synthesis. Mutations causing resistance to catabolite repression in B. subtilis GLU-47, SF33, WLN30, and WLN104 also relieved catabolite repression of amyRi-lacZ.

Two developmental genes encoding sigma factor homologs are arranged in tandem in Bacillus subtilis

The sporulation-essential gene spoIIG of the Gram-positive bacterium Bacillus subtilis encodes the sporulation-specific sigma factor sigma 29(sigma E). We report here the initial characterization of a gene, referred to as ORF3, located immediately downstream of the spoIIG gene. The results indicate that ORF3 encodes a sigma homolog, whose expression is highly regulated during development. Analysis of the ORF3 nucleotide sequence reveals an open reading frame encoding a polypeptide of 260 amino acid residues (molecular mass of 30.1 kDa). Its predicted amino acid sequence shows significant similarity to that of other RNA polymerase sigma factor sequences. S1 nuclease mapping experiments indicate that ORF3 is initially cotranscribed with spoIIG from about 1 to 4 hr into the sporulation process and that later on ORF3 is transcribed independently from a new site located between spoIIG and ORF3. The role of ORF3 was investigated by constructing a deletion mutation in its structural gene. The mutant exhibits normal growth but is unable to produce heat-resistant spores. We propose that the ORF3 gene product is a sigma factor or a related peptide essential for sporulation at a late stage of development.

Early-blocked sporulation mutations alter expression of enzymes under carbon control in Bacillus subtilis

The physiological roles of the gene subset defined by early-blocked sporulation mutations (spo0) and their second-site suppressor alleles (rvtA11 and crsA47) remain cryptic for both vegetative and sporulating Bacillus subtilis cells. To test the hypothesis that spo0 gene products affect global regulation, we assayed the levels of carbon- and nitrogen-sensitive enzymes in wild-type and spo0 strains grown in a defined minimal medium containing various carbon and nitrogen sources. All the spo0 mutations (except spo0J) affected both histidase and arabinose isomerase levels in an unexpected way: levels of both carbon-sensitive enzymes were two- to six-fold higher in spo0 strains compared to wild type, when cells were grown on the derepressing carbon sources arabinose or maltose. There was no difference in enzyme levels with glucose-grown cells, nor was there a significant difference in levels of the carbon-independent enzymes glutamine synthetase and glucose-6-phosphate dehydrogenase. This effect was not due to a slower growth rate for the spo0 mutants on the poor carbon and nitrogen sources used. The levels of carbon-sensitive enzymes were not simply correlated with sporulation ability in genetically suppressed spo0 mutants, but the rvtA and crsA suppressors each had such marked effects on wild-type growth and enzyme levels that these results were difficult to interpret. We conclude that directly or indirectly the spo0 mutations, although blocking the sporulation process, increase levels of carbon-sensitive enzymes, possibly at the level of gene expression.

Promoter switching during development and the termination site of the sigma 43 operon of Bacillus subtilis

Sequencing data indicated that the RNA polymerase sigma 43 operon of Bacillus subtilis consisted of three genes, P23 (function unknown), dnaE (DNA primase), and rpoD (sigma 43) (Wang and Doi 1986a). S1 nuclease mapping experiments with RNA from various stages of growth demonstrated the presence of two overlapping sigma 43 promoters that controlled the expression of the operon during growth and a sigma 37 promoter that regulated the expression of the operon during the sporulation phase. This promoter switching mechanism ensured that this important operon would be expressed during different nutritional states of the cell and also illustrated a function for the minor RNA polymerase sigma 37 holoenzyme in the expression of genes which are normally expressed during the logarithmic phase of growth. The location of the transcription termination signal confirmed that the sigma 43 operon consists of three genes.

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

We have constructed spo0A-lacZ and spo0F-lacZ fusions with a temperate phage vector and have investigated how spo0 gene products are involved in the expression of each of these genes. The expression of spo0A-lacZ and spo0F-lacZ was stimulated at about the time of cessation of vegetative growth in Spo+ cells. This stimulation of spo0A-lacZ was impaired by mutations in the spo0B, D, E, F or H genes but was not affected by mutations in the spo0J or K genes. Similar results were obtained with the spo0F-lacZ fusion. The effect of the spo0A mutation on spo0A-lacZ expression was characteristic: the spo0A-directed beta-galactosidase activity found during vegetative growth was significantly enhanced in the spo0A mutant. This result suggests that spo0A gene expression is auto-regulated being repressed by its own gene product. Another remarkable observation was the effect of the sof-1 mutation, which is known to be a spo0A allele; it suppressed the sporulation deficiency of spo0B, spo0D and spo0F mutants. The spo0A-lacZ stimulation, which is impaired by any one of these spo0 mutations, was restored by the additional sof-1 mutation.