Intergenic suppression of spoO phenotypes by the Bacillus subtilis mutation rvtA

Proteolysis of the replication checkpoint protein Sda is necessary for the efficient initiation of sporulation after transient replication stress in Bacillus subtilis

Cells of Bacillus subtilis actively co-ordinate the initiation of sporulation with DNA replication and repair. Conditions that perturb replication initiation or replication elongation induce expression of a small protein, Sda, that specifically inhibits the histidine kinases required to initiate spore development. Previously, the role of Sda has been studied during chronic blocks to DNA replication. Here we show that induction of Sda is required to delay the initiation of sporulation when replication elongation is transiently blocked or after UV irradiation. During the recovery phase, cells efficiently sporulated, but this required the proteolysis of Sda. The rapid proteolysis of Sda required the ClpXP protease and the uncharged C-terminal sequence of Sda. Replacing the last two residues of Sda, both serines, with aspartic acids markedly stabilized Sda. Strains expressing sdaDD from the endogenous sda locus were unable to efficiently initiate sporulation after transient replication stress. We conclude that the Sda replication checkpoint is required to delay the initiation of sporulation when DNA replication is transiently perturbed, and that the intrinsic instability of Sda contributes to shutting off the pathway. The Sda checkpoint thus co-ordinates early events of spore development, including the polar cell division, with successful completion of chromosome replication.

A Checkpoint Protein That Scans the Chromosome for Damage at the Start of Sporulation in Bacillus subtilis

In response to DNA damage, cells activate checkpoint signaling cascades to control cell-cycle progression and elicit DNA repair in order to maintain genomic integrity. The sensing and repair of lesions is critical for Bacillus subtilis cells entering the developmental process of sporulation as damaged DNA may prevent the cells from completing spore morphogenesis. We report the identification of the protein DisA (DNA integrity scanning protein, annotated YacK), which is required to delay the initiation of sporulation in response to chromosomal damage. DisA is a nonspecific DNA binding protein that forms a single focus, which moves rapidly within the bacterial cell, pausing at sites of DNA damage. We propose that the DisA focus scans along the chromosomes searching for lesions. Upon encountering a lesion, DisA delays entry into sporulation until the damage is repaired.

A search for amino acid substitutions that universally activate response regulators

Two-component regulatory systems, typically composed of a sensor kinase to detect a stimulus and a response regulator to execute a response, are widely used by microorganisms for signal transduction. Response regulators exhibit a high degree of structural similarity and undergo analogous activating conformational changes upon phosphorylation. The activity of particular response regulators can be increased by specific amino acid substitutions, which either prolong the lifetime or mimic key features of the phosphorylated state. We probed the universality of response regulator activation by amino acid substitution. Thirty-six mutations that activate 11 different response regulators were identified from the literature. To determine whether the activated phenotypes would be retained in the context of a different response regulator, we recreated 51 analogous amino acid substitutions at corresponding positions of CheY. About 55% of the tested substitutions completely or partially inactivated CheY, approximately 30% were phenotypically silent, and approximately 15% activated CheY. Three previously uncharacterized activated CheY mutants were found. The 94NS (and presumably 94NT) substitutions resulted in resistance to CheZ-mediated dephosphorylation. The 113AP substitution led to enhanced autophosphorylation and may increase the fraction of non-phosphorylated CheY molecules that populate the activated conformation. The locations of activating substitutions on the response regulator three-dimensional structure are generally consistent with current understanding of the activation mechanism. The best candidates for potentially universal activating substitutions of response regulators identified in this study were 13DK and 113AP.

Postexponential regulation of sin operon expression in Bacillus subtilis

The expression of many gene products required during the early stages of Bacillus subtilis sporulation is regulated by sinIR operon proteins. Transcription of sinIR from the P1 promoter is induced at the end of exponential growth. In vivo transcription studies suggest that P1 induction is repressed by the transition-state regulatory protein Hpr and is induced by the phosphorylated form of Spo0A. In vitro DNase I footprinting studies confirmed that Hpr, AbrB, and Spo0A are trans-acting transcriptional factors that bind to the P1 promoter region of sinIR. We have also determined that the P1 promoter is transcribed in vitro by the major vegetative sigma factor, final sigma(A), form of RNA polymerase.

In vivo effects of sporulation kinases on mutant Spo0A proteins in Bacillus subtilis

The phosphorylated form of the response regulator Spo0A (Spo0A~P) is required for the initiation of sporulation in Bacillus subtilis. Phosphate is transferred to Spo0A from at least four histidine kinases (KinA, KinB, KinC, and KinD) by a phosphotransfer pathway composed of Spo0F and Spo0B. Several mutations in spo0A allow initiation of sporulation in the absence of spo0F and spo0B, but the mechanisms by which these mutations allow bypass of spo0F and spo0B are not fully understood. We measured the ability of KinA, KinB, and KinC to activate sporulation of five spo0A mutants in the absence of Spo0F and Spo0B. We also determined the effect of Spo0E, a Spo0A~P-specific phosphatase, on sporulation of strains containing the spo0A mutations. Our results indicate that several of the mutations relax the specificity of Spo0A, allowing Spo0A to obtain phosphate from a broader group of phosphodonors. In the course of these experiments, we observed medium-dependent effects on the sporulation of different mutants. This led us to identify a small molecule, acetoin, that can stimulate sporulation of some spo0A mutants.

Control of sporulation gene expression in Bacillus subtilis by the chromosome partitioning proteins Soj (ParA) and Spo0J (ParB)

Two chromosome partitioning proteins, Soj (ParA) and Spo0J (ParB), regulate the initiation of sporulation in Bacillus subtilis. In a spo0J null mutant, sporulation is inhibited by the action of Soj. Soj negatively regulates expression of several sporulation genes by binding to the promoter regions and inhibiting transcription. All of the genes known to be inhibited by Soj are also activated by the phosphorylated form of the transcription factor Spo0A (Spo0A approximately P). We found that, in a spo0J null mutant, Soj affected sporulation, in part, by decreasing the level of Spo0A protein. Soj negatively regulated transcription of spo0A and associated with the spo0A promoter region in vivo. Expression of spo0A from a heterologous promoter in a spo0J null mutant restored Spo0A levels and partly bypassed the sporulation and gene expression defects. Soj did not appear to significantly affect phosphorylation of Spo0A. Thus, in the absence of Spo0J, Soj inhibits sporulation and sporulation gene expression by inhibiting accumulation of the activator protein Spo0A and by acting downstream of Spo0A to inhibit gene expression directly.

Control of initiation of sporulation by replication initiation genes in Bacillus subtilis

Initiation of spore formation in Bacillus subtilis appears to depend on initiation of DNA replication. This regulation was first identified using a temperature-sensitive mutation in dnaB. We found that mutations in the replication initiation genes dnaA and dnaD also inhibit sporulation, indicating that inhibition of sporulation is triggered by general defects in the function of replication initiation proteins.

Alanine mutants of the Spo0F response regulator modifying specificity for sensor kinases in sporulation initiation

Five single alanine substitution mutations in the Spo0F response regulator gave rise to mutant strains of Bacillus subtilis with seemingly normal sporulation that nevertheless rapidly segregated variants blocked in sporulation. The basis for this deregulated phenotype was postulated to be increased phosphorylation of the Spo0A transcription factor, resulting from enhanced phosphate input or decreased dephosphorylation of the phosphorelay. Strains bearing two of these Spo0F mutant proteins, Y13A and I17A, retained a requirement for KinA and KinB kinases in sporulation, whereas the remaining three, L66A, I90A and H101A, gave strains that sporulated well in the absence of both KinA and KinB. Sporulation of strains bearing L66A and H101A mutations was decreased in a mutant lacking KinA, KinB and KinC, but the strain bearing the I90A mutation required the further deletion of KinD to lower its sporulation frequency. The affected residues, L-66, I-90 and H-101, are involved in crucial hydrophobic contacts stabilizing the orientation of helix alpha4 of Spo0F. The data are consistent with the notion that these three mutations alter the conformation of the beta4-alpha4 loop of Spo0F that is known to contain residues critical for KinA:Spo0F recognition. As this loop has a propensity for multiple conformations, the spatial arrangement of this loop may play a critical role in kinase selection by Spo0F and might be altered by regulatory molecules interacting with Spo0F.

sigmaK can negatively regulate sigE expression by two different mechanisms during sporulation of Bacillus subtilis

Temporal and spatial gene regulation during Bacillus subtilis sporulation involves the activation and inactivation of multiple sigma subunits of RNA polymerase in a cascade. In the mother cell compartment of sporulating cells, expression of the sigE gene, encoding the earlier-acting sigma factor, sigmaE, is negatively regulated by the later-acting sigma factor, sigmaK. Here, it is shown that the negative feedback loop does not require SinR, an inhibitor of sigE transcription. Production of sigmaK about 1 h earlier than normal does affect Spo0A, which when phosphorylated is an activator of sigE transcription. A mutation in the spo0A gene, which bypasses the phosphorelay leading to the phosphorylation of Spo0A, diminished the negative effect of early sigmaK production on sigE expression early in sporulation. Also, early production of sigmaK reduced expression of other Spo0A-dependent genes but not expression of the Spo0A-independent ald gene. In contrast, both sigE and ald were overexpressed late in development of cells that fail to make sigmaK. The ald promoter, like the sigE promoter, is believed to be recognized by sigmaA RNA polymerase, suggesting that sigmaK may inhibit sigmaA activity late in sporulation. To exert this negative effect, sigmaK must be transcriptionally active. A mutant form of sigmaK that associates with core RNA polymerase, but does not direct transcription of a sigmaK-dependent gene, failed to negatively regulate expression of sigE or ald late in development. On the other hand, the negative effect of early sigmaK production on sigE expression early in sporulation did not require transcriptional activity of sigmaK RNA polymerase. These results demonstrate that sigmaK can negatively regulate sigE expression by two different mechanisms, one observed when sigmaK is produced earlier than normal, which does not require sigmaK to be transcriptionally active and affects Spo0A, and the other observed when sigmaK is produced at the normal time, which requires sigmaK RNA polymerase transcriptional activity. The latter mechanism facilitates the switch from sigmaE to sigmaK in the cascade controlling mother cell gene expression.

Effects of spo0 mutations on spo0A promoter switching at the initiation of sporulation in Bacillus subtilis

Transcriptional analyses of the Bacillus subtilis sporulation initiator gene spo0A revealed that promoter switching from the vegetative (Pv) to the sporulation-specific (Ps) promoter did not occur in the spo0A, spo0B, spo0E, spo0F, and spo0H mutants. The sof-1 mutation in spo0A restored the promoter switching in the spo0F mutant. These results strongly suggest that Spo0A plays a central role in the regulation of its own promoter switching.

Possible role for the essential GTP-binding protein Obg in regulating the initiation of sporulation in Bacillus subtilis

We fused obg, encoding an essential GTP-binding protein in Bacillus subtilis, to the LacI-repressible, IPTG (isopropyl-beta-D-thiogalactopyranoside)-inducible promoter Pspac. Depletion of Obg, following removal of IPTG, caused a defect in sporulation and in expression of sporulation genes that are activated by Spo0A approximately P. These defects were significantly relieved by a mutation in spo0A (rvtA11) that bypasses the normal phosphorylation pathway, indicating that Obg might normally be required, either directly or indirectly, to stimulate activity of the phosphorelay that activates Spo0A.

Analysis of a suppressor mutation ssb (kinC) of sur0B20 (spo0A) mutation in Bacillus subtilis reveals that kinC encodes a histidine protein kinase

sur0B20 is a mutation that suppresses the effects of spo0B delta B or spo0F221 mutations in Bacillus subtilis, sur0B20 is an allele of the spo0A gene (Glu-14 to Val-14 conversion) and restores the sporulation of spo0B or spo0F mutants to the wild-type level. Here, we report the isolation of suppressor mutations of sur0B20 (ssb). One of these mutations, ssb-12, severely impairs the suppressor activity of sur0B20. A 2.5-kbp MboI fragment which complements the ssb-12 mutation was cloned by the prophage transformation method using phi CM as a vector. Nucleotide sequencing of the fragment revealed two open reading frames (orf1 and orf2). Gene disruption and complementation experiments showed that orf2 is the ssb gene. ssb was shown to encode a protein with a molecular weight of 48,846 (428 amino acid residues) showing strong similarity to transmitter kinases, especially KinA, of two-component regulatory systems. Therefore, ssb was renamed kinC. Deletion of kinC had no observable effect on sporulation. kinC transcription was induced at the onset of sporulation, probably from a sigma A-dependent promoter, and its expression was shut off at T3. DNase I protection experiments showed that the Spo0A protein binds to two adjoining sites in the kinC promoter region with different affinities. These results suggest that kinC expression might be regulated by Spo0A.

Isolation and characterization of kinC, a gene that encodes a sensor kinase homologous to the sporulation sensor kinases KinA and KinB in Bacillus subtilis

Phosphorylation of the transcription factor encoded by spo0A is required for the initiation of sporulation in Bacillus subtilis. Production and accumulation of Spo0A-P is controlled by histidine protein kinases and the spo0 gene products. To identify additional genes that might be involved in the initiation of sporulation and production of Spo0A-P, we isolated genes which when present on a multicopy plasmid could suppress the sporulation defect of a spo0K mutant. kinC was one gene isolated in this way. A multicopy plasmid containing kinC completely or partially suppressed the sporulation defect caused by mutations in spo0K, kinA, spo0F, and spo0B, indicating that at least when overexpressed, KinC is capable of stimulating phosphorylation of Spo0A independently of the normal phosphorylation pathway. The predicted product of kinC is 428 amino acids long and is most similar to KinA and KinB, the histidine protein kinases involved in the initiation of sporulation. In otherwise wild-type strains, kinC null mutations caused little or no defect in sporulation under the conditions tested. However, in the absence of a functional phosphorelay (spo0F or spo0B), KinC appears to be the kinase responsible for phosphorylation of the sof-1 and rvtA11 forms of Spo0A.

spo0J is required for normal chromosome segregation as well as the initiation of sporulation in Bacillus subtilis

The spo0J gene of Bacillus subtilis is required for the initiation of sporulation. We show that the sporulation defect caused by null mutations in spo0J is suppressed by a null mutation in the gene located directly upstream from spo0J, soj (suppressor of spo0J). These results indicate that Soj inhibits the initiation of sporulation and that Spo0J antagonizes that inhibition. Further genetic experiments indicated that Soj ultimately affects sporulation by inhibiting the activation (phosphorylation) of the developmental transcription factor encoded by spo0A. In addition, the temperature-sensitive sporulation phenotype caused by the ftsA279 (spoIIN279) mutation was partly suppressed by the soj null mutation, indicating that FtsA might also affect the activity of Soj. Soj and Spo0J are known to be similar in sequence to a family of proteins involved in plasmid partitioning, including ParA and ParB of prophage P1, SopA and SopB of F, and IncC and KorB of RK2, spo0J was found to be required for normal chromosome partitioning as well as for sporulation. spo0J null mutants produced a significant proportion of anucleate cells during vegetative growth. The dual functions of Spo0J could provide a mechanism for regulating the initiation of sporulation in response to activity of the chromosome partition machinery.

Activation of spo0A transcription by sigma H is necessary for sporulation but not for competence in Bacillus subtilis

spo0A and spo0H are needed for the initiation of sporulation and for the development of genetic competence in Bacillus subtilis. Transcription of spo0A initiates from two promoters, Pv and Ps. Pv is active during vegetative growth and is recognized by RNA polymerase containing sigma A. Expression from Ps increases during sporulation and depends on sigma H, the spo0H gene product. A deletion mutation, spo0A delta Ps, that removes the promoter controlled by sigma H blocked sporulation but had no detectable effect on competence. These results indicate that expression of spo0A from Ps is necessary for sporulation and that the requirement for spo0H in competence development is not due to its role in expression of spo0A.

Integration of multiple developmental signals in Bacillus subtilis through the Spo0A transcription factor

Multiple physiological and environmental signals are needed to initiate endospore formation in Bacillus subtilis. One key event controlling sporulation is activation of the Spo0A transcription factor. Spo0A is a member of a large family of conserved regulatory proteins whose activity is controlled by phosphorylation. We have isolated deletion mutations that remove part of the conserved amino terminus of Spo0A and make the transcription factor constitutively active, indicating that the amino terminus normally functions to keep the protein in an inactive state. Expression of an activated gene product is sufficient to activate expression of several sporulation genes in the absence of signals normally needed for initiation of sporulation. Our results indicate that nutritional, cell density, and cell-cycle signals are integrated through the phosphorylation pathway that controls activation of Spo0A.

The phosphorelay signal transduction pathway in the initiation of Bacillus subtilis sporulation

The formation of spores in Bacillus subtilis is a developmental process under genetic control. The decision to either divide or sporulate is regulated by the state of phosphorylation of the SpoOA transcription factor. Phosphorylated SpoOA (SpoOA approximately P) is both a repressor and an activator of transcription depending on the promoter it is affecting. SpoOA approximately P is the end product of the phosphorelay, a signal transduction system linking environmental information to the activation of sporulation. Activation or deinhibition of two ATP-dependent kinases, KinA and KinB, to phosphorylate the SpoOF secondary messenger initiates the phosphorelay. SpoOF approximately P is the substrate for the SpoOB protein, a phosphoprotein phosphotransferase which transfers the phosphate group to SpoOA. The SpoOA approximately P formed from this pathway orchestrates transcription events during the initial stage of spore development through direct effects on a variety of promoters and through the use of other transcription factors, termed transition state regulators, whose activity it controls. Because commitment to sporulation has serious cellular programming consequences and is not undertaken capriciously, the phosphorelay is subject to a variety of complex controls on the flow of phosphate through its components.

cis-unsaturated fatty acids specifically inhibit a signal-transducing protein kinase required for initiation of sporulation in Bacillus subtilis

The initiation of sporulation in Bacillus subtilis is controlled by the Spo0A transcription factor which is activated by phosphorylation through a phosphorelay mechanism that is dependent upon the activity of one or more protein kinases. The enzymatic activity of one of these protein kinases, KinA, was found to be inhibited in vitro by certain fatty acids. The most potent inhibitors have at least one unsaturated double bond in the cis configuration and a chain length of 16-20 carbon atoms. Homologous isomers with a trans double bond are not inhibitory. Saturated straight- or branched-chain fatty acids are either much weaker inhibitors or have no effect. The inhibitors prevent autophosphorylation of KinA and are non-competitive with ATP. B. subtilis phospholipids were found to contain at least one as yet unidentified type of fatty acid that, when present in an unesterified form, inhibited KinA. The results suggest that the concentration of a specific unsaturated fatty acid may act as a signal linking the initiation of sporulation to the status of membrane synthesis and septation or some other specific membrane-associated activity.

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.

Suppression of defective-sporulation phenotypes by mutations in transcription factor genes of Bacillus subtilis

Mutations in the Bacillus subtilis major RNA polymerase sigma factor gene (rpoD/crsA47) and a sensory receiver gene (spoOA/rvtA11) are potent intergenic suppressors of several stage 0 sporulation mutations (spoOB, OE, OF & OK). We show here that these suppressors also rescue temperature-sensitive sporulation phenotypes (Spots) caused by mutations in RNA polymerase, ribosomal protein, and protein synthesis elongation factor EF-G genes. The effects of the crsA and rvtA suppressors on RNA polymerase and ribosomal protein spots mutations are similar to those previously described for mutations in another intergenic suppressor gene rev. We have examined the effects of rvtA and crsA mutations on the expression of sporulation-associated membrane proteins, including flagellin and penicillin binding protein 5* (PBP 5*). Both suppressors restored sporulation and synthesis of PBP 5* in several spoO mutants. However, only rvtA restored flagellin synthesis in spoO suppressed backgrounds. The membrane protein phenotypes resulting from the presence of crsA or rvtA suppressors in spoO strains suggests that these suppressors function via distinct molecular mechanisms. The rvtA and crsA mutations are also able to block the ability of ethanol to induce spoO phenocopies at concentrations of ethanol which prevent sporulation in wild type cells. The effects of ethanol on sporulation-associated membrane protein synthesis in wild type and suppressor containing strains have been examined.

The spo0K locus of Bacillus subtilis is homologous to the oligopeptide permease locus and is required for sporulation and competence

Spore formation in Bacillus subtilis is a dramatic response to environmental signals that is controlled in part by a two-component regulatory system composed of a histidine protein kinase (SpoIIJ) and a transcriptional regulator (Spo0A). The spo0K locus plays an important but undefined role in the initiation of sporulation and in the development of genetic competence. spoIIJ spo0K double mutants had a more severe defect in sporulation than either single mutant. Overproduction of the spoIIJ gene product resulted in the suppression of the sporulation defect, but not the competence defect, caused by mutations in the spo0K locus. On the basis of the phenotype of the spoIIJ spo0K double mutant and the effect of overproduction of the spoIIJ gene product, a transposon insertion in the spo0K locus was isolated. The spo0K locus was cloned and sequenced. spo0K proved to be an operon of five genes that is homologous to the oligopeptide permease (opp) operon of Salmonella typhimurium and related to a large family of membrane transport systems. The requirement for the transport system encoded by spo0K in the development of competence was somewhat different than its requirement in the system encoded by spo0K in the development of competence was somewhat different than its requirement in the initiation of sporulation. Disruption of the last open reading frame in the spo0K operon caused a defect in competence but had little or no effect on sporulation. We hypothesize that the transport system encoded by spo0K may have a role in sensing extracellular peptide factors that we have shown are required for efficient sporulation and perhaps in sensing similar factors that may be necessary for genetic competence.

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.

Structural alterations in the Bacillus subtilis Spo0A regulatory protein which suppress mutations at several spo0 loci

Secondary site mutations that restore sporulation to sporulation-defective spo0F or spo0B deletion mutants were found to reside in the spo0A gene. Sequence analysis of 23 such sof mutants showed that the sof mutations fell into six classes of missense codon changes, primarily in the conserved amino-terminal domain of the response regulator Spo0A protein. Changes were observed in codons 12, 14, 60, 92, and 121. The residues affected were predominantly located in the potential turn regions at one end of the amino-terminal conserved domain on the same topological face as the active site aspartate residues. The ability of sof mutations to suppress deficiencies in the transmitter kinases, KinA and KinB, of two-component regulatory systems was tested. All of the sof mutations suppressed the sporulation deficiency of kinA mutants but only two classes among five tested suppressed kinB mutations. sof mutants segregated Spo- colonies at high frequency. Five of these Spo- mutants were found to result from mutations in the spo0A locus that reversed the effect of the sof mutatation. One of these was sequenced and found to have the original sof mutation and a new mutation, sos, at codon 105. The accumulation of sos mutations in sof strains suggested that the sof mutations have a subtle, yet deleterious, effect on the growth of the cell. The results suggested that the sof mutations increase the avidity for or reactivity with transmitter kinases in an allele-specific manner, although in some cases it is possible that the sof mutations obviate the need for phosphorylation to activate the Spo0A protein. An alternative hypothesis is presented in which the sof mutations play the role of bypass mutations for kinases.

Defects in the nutrient-dependent methylation of a membrane-associated protein in spo mutants of Bacillus subtilis

Methylation of a membrane-associated protein with an apparent molecular mass of 40,000 daltons has been observed in Bacillus subtilis. The methylation was nutrient dependent and occurred with a doubling time of 4 +/- 1 min. In wild-type strains, the half-life of turnover of the methyl group(s) was 17 +/- 6 min. Several isogenic strains of B. subtilis containing spo0 mutations (spo0A and spo0H) were found to be normal in glutamate-dependent methylation of the protein and turnover of the methyl group(s). In strains containing spo0B and spo0E mutations, the methyl group(s) were incorporated in response to glutamate addition but turnover was not at a normal rate. The half-life of methyl group turnover was extended to 45 +/- 3 min in these strains. In a spo0K mutant and in spoIIJ and spoIIF mutants, the protein was not significantly methylated. The methylation of a 40,000 dalton protein was also found to be dependent on phosphate. This methylation was observed in wild-type and spo0A and spo0H strains with a doubling time of 4 +/- 1 min and a half-life of turnover of the methyl group(s) of 11 +/- 3 min. In strains containing spo0B, spo0E, and spo0F mutations, the phosphate-dependent incorporation of the methyl group(s) was normal (5 +/- 1 min) but the turnover half-life was extended to 46 +/- 8 min. It is not known whether the nitrogen-dependent and phosphate-dependent systems methylated the same protein.(ABSTRACT TRUNCATED AT 250 WORDS)

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.

Isolation and sequence of the spo0E gene: its role in initiation of sporulation in Bacillus subtilis

The pleiotropic stage 0 sporulation locus spo0E was isolated and sequenced. The spo0E gene was found to code for a protein of 9791 molecular weight. Two spo0E mutations were identified by sequence analysis and were found to give rise to nonsense codons within the gene. The results indicated that it is the lack of the spo0E gene product that is responsible for the sporulation-defective phenotype. The DNA fragment containing the spo0E locus was inhibitory to sporulation when present on a multicopy plasmid. Since DNA fragments containing only the upstream region of the gene were also inhibitory, this effect was not due to over-production of the spo0E gene product. Coupling the transcription of the spo0E gene to beta-galactosidase in an integrative plasmid vector revealed that active transcription of this gene begins at the end of exponential growth and continues through the early part of sporulation. Studies of the regulation of this gene have allowed the generation of a hypothesis to explain the interactions of those five stage 0 genes involved in the activation of sporulation-specific transcription.

Characterization of heat shock in Bacillus subtilis

We characterized the general properties of the heat shock response in Bacillus subtilis W168, B. subtilis JH642, and an spo0A mutant by using pulse-labeling of bacterial proteins and one-dimensional sodium dodecyl sulfate-polyacrylamide gel electrophoresis. The transfer of cells from 37 to 50 degrees C repressed synthesis of most cellular proteins and led to the induction of at least 26 distinct heat shock proteins after about 3 min. Ethanol (4% [vol/vol]) induced a similar set of proteins, but somewhat more slowly. Synthesis of the majority of heat shock proteins at 50 degrees C returned to a steady-state level 20 to 40 min after the shock. Although no B. subtilis heat shock protein has yet been extensively characterized, three of these proteins were found to be immunologically related to the Escherichia coli heat shock proteins Dnak, Lon, and GroEL. Synthesis of both sigma 28 and sigma 43 proteins was sharply reduced during heat shock. Although a spo0A amber mutation blocks transcription from promoters used by at least two minor B. subtilis sigma factors, it did not alter the kinetics or general properties of the heat shock response.

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.

Bacillus thuringiensis var. israelensis delta-endotoxin. Cloning and expression of the toxin in sporogenic and asporogenic strains of Bacillus subtilis

A plasmid-borne gene from Bacillus thuringiensis var. israelensis encoding a 27,340 Mr insecticidal delta-endotoxin has been cloned on a bifunctional multicopy plasmid in a wild-type sporogenic strain and two asporogenic mutants of Bacillus subtilis. The delta-endotoxin gene is expressed at a low level during vegetative growth in all three strains, but the synthesis of the toxin increases markedly during the third hour of stationary phase for both the sporogenic strain and an asporogenic mutant containing the OJ lesion. However, in a stage OA mutant, this increase in delta-endotoxin synthesis is not observed. In both the wild-type sporogenic B. subtilis and the asporogenic OJ strain, phase-bright inclusions, resembling the israelensis crystal in appearance, are visible during late stationary phase. The insoluble inclusions from the B. subtilis transformants, consisting solely of the 27,340 Mr polypeptide, were purified by density gradient centrifugation and found to be extremely toxic to Aedes aegypti larvae. After solubilization in alkaline buffer, this polypeptide was also shown to be haemolytic for human erythrocytes and to lyse Aedes albopictus cells with the same LC50 value as native israelensis delta-endotoxin crystals. During stationary phase, novel mRNA species appear in both the wild-type strain and the OJ mutant, but not in the OA mutant, and these appear to be the major gene-specific transcripts. Transcriptional mapping of delta-endotoxin-specific mRNA has shown that the same region of initiation is used at a relatively low level in all three strains during vegetative growth.

Genetic mapping of rpoD implicates the major sigma factor of Bacillus subtilis RNA polymerase in sporulation initiation

We have mapped the chromosomal locus of rpoD, which encodes the major sigma factor of Bacillus subtilis RNA polymerase. The rpoD locus lay between aroD and lys, tightly linked to dnaE and inseparable from crsA. Marker order in this region was acf-aroD-dnaE-rpoD(crsA)-spoOG-lys. By transformation using cloned donor DNA from the rpoD region, we identified the gene immediately upstream of rpoD as dnaE, which coded for a 62,000 dalton protein essential for DNA replication. Both dnaE and rpoD were transcribed in the same direction, counterclockwise on the chromosome. The gene functions and organization in the rpoD region are thus similar to those of the E. coli sigma operon. We also used transformation to identify crsA47 as a mutation within the sigma coding region itself. The crsA alteration of sigma renders the sporulation process insensitive to glucose catabolite repression, and also restores sporulation ability to strains carrying early-blocked spoOE, spoOF, and spoOK mutations. Thus the major sigma factor and these spoO gene products directly or indirectly affect the same cellular function.

Suppression of defective-sporulation phenotypes by mutations in the major sigma factor gene (rpoD) of Bacillus subtilis

Mutations (crsA47 and crsA4) in the major sigma factor gene (rpoD) of Bacillus subtilis RNA polymerase have been found to be powerful intergenic suppressors of spoOB, spoOE, spoOF, spoOK and spoIIG mutations. The crsA47 suppressor restores sporulation of spoOE, spoOF, spoOK and spoIIG mutants to levels near those of wild type bacteria and substantially improves the sporulation of a spoOB strain. The crsA mutations are shown to prevent the induction by aliphatic alcohols of SpoO phenocopies in wild type B. subtilis cells.

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.