Passage to nonselective media transiently alters growth of mycophenolic acid-resistant mammalian cells expressing the escherichia coli xanthine-guanine phosphoribosyltransferase gene: implications for sequential selection strategies

The Escherichia coli xanthine-guanine phosphoribosyltransferase gene (Ecogpt) rescues mammalian cells from inhibition of purine nucleotide biosynthesis by mycophenolic acid (MPA). We used Ecogpt and other selectable markers to obtain subclones of NIH 3T3 derivatives (EN/NIH) stably expressing transfected genes of interest. In their respective selective mediums, growth of MPA-resistant (MPA(R)) isolates was indistinguishable from that of aminoglycoside-resistant counterparts expressing selectable marker genes conferring resistance to protein synthesis inhibitors hygromycin B, puromycin, and G418. Growth of aminoglycoside-resistant isolates remained unaltered on passage to nonselective media. In contrast, MPA(R) cells transferred from MPA complete media to nonselective media displayed morphologic changes with static growth. These findings resolved completely by third passage in nonselective media and were independent of the gene of interest cis-linked to the selectable marker. Sequential selection strategies involving cell culture conditions resulting in these altered growth characteristics significantly impaired detection (by selection in G418) of genomic events associated with reactivation of enhancerless, transcriptionally silent neointegrants present in MPA(R) EN/NIH isolates. We explored the cause of these cell culture findings and defined transfection and sequential selection strategies for MPA(R) derivatives that successfully circumvented these effects.

sigma E changed to sigma B specificity by amino acid substitutions in its -10 binding region

The association of a sigma factor (sigma) with RNA polymerase in bacteria determines its specificity of promoter utilization. To identify amino acid residues in sigma E from Bacillus subtilis that determine the specificity of its interaction with the nucleotides at the -10 region of its cognate promoters, we tested whether base pair substitutions in the -10 region of a sigma B-dependent promoter could signal its utilization by sigma E-RNA polymerase. We found that a combination of base pair substitutions at positions -15 and -14 of the sigma B-dependent ctc promoter resulted in its utilization by sigma E-RNA polymerase in vivo. We also found that the combination of two amino acid substitutions at positions 119 and 120 in sigma E changed its specificity for promoter utilization, resulting in a sigma factor that directed transcription from the sigma B-dependent ctc promoter, but not from sigma E-dependent promoters. These results suggest that amino acid residues at positions 119 and 120 determine, at least in part, the specificity of interactions between sigma E and the nucleotides in the -10 region of its cognate promoters.

Sequence-specific interactions between promoter DNA and the RNA polymerase sigma factor E

In order to determine which amino acyl residues in a secondary sigma factor govern its specificity of recognition at the -35 region of promoters, we examined the effects of amino acid substitutions in sigma E in Bacillus subtilis that made the sequence of its putative -35 recognition region more similar to another sigma factor in B. subtilis, sigma K. We found that a single amino acid substitution at position 217 of sigma E resulted in a sigma factor that could direct transcription from sigma K-dependent promoters. Furthermore, we tested whether this amino acid substitution in sigma E had changed the specificity of interactions of the sigma with -35 region sequences by examining the activity of the mutant sigma E on derivatives of sigma E-dependent promoters that contained single base-pair substitutions. We found that this substitution in sigma E specifically suppressed the effect of a single base-pair substitution at position -31 in a sigma E-dependent promoter spoIIID. The amino acyl residue at another position (219) on sigma E affected the specificity of interaction with position -33 in spoIIID promoter. The amino acyl residues at the two positions in sigma E, 217 and 219, that determine the specificity of interactions between the sigma and base-pairs in the -35 region of its cognate promoters (positions -33 and -31, respectively, in the spoIIID promoter) probably closely contact these base-pairs.

Evidence that the transcriptional activator Spo0A interacts with two sigma factors in Bacillus subtilis

The transcriptional regulator Spo0A activates transcription from two types of promoters. One type of promoter is used by RNA polymerase containing sigma A, whereas the other type is used by RNA polymerase containing sigma H. There are Spo0A-binding sites near the -35 region of both types of promoters. It has been reported that some transcriptional regulators that bind near the -35 regions of promoters directly interact with the sigma subunit of RNA polymerase. Therefore, we looked for evidence that Spo0A interacts with both sigma factors by searching for single amino acid substitutions in these factors that specifically prevent expression from Spo0A-dependent promoters, but that do not decrease activity of Spo0A-independent promoters. Two such amino acid substitutions were isolated in sigma A and one was isolated in sigma H. The amino acid substitutions in sigma A prevented expression from the Spo0A-activated promoters, spoIIG and spoIIE, but expression was not impaired from the Spo0A-independent, sigma A-dependent promoter tms or from the Spo0A-activated, sigma H-dependent promoter, spoIIA. The amino acid substitution in sigma H prevented expression from the spoIIA promoter but not from the Spo0A-independent promoter, citGp2, which is used by sigma H-RNA polymerase. All of these amino acid substitutions occur in the carboxyl terminus of the sigma factors. These amino acid substitutions may define the sites of contact between the sigma factors and Spo0A. The ability of response regulators such as Spo0A to interact with multiple sigma factors may increase the variety of responses made by bacteria using a limited number of transcription factors.

A single amino acid substitution in sigma E affects its ability to bind core RNA polymerase

We have examined the role of the most highly conserved region of bacterial RNA polymerase sigma factors by analyzing the effect of amino acid substitutions and small deletions in sigma E from Bacillus subtilis. sigma E is required for the production of endospores in B. subtilis but not for vegetative growth. Strains expressing each of several mutant forms of sigE were found to be deficient in their ability to form endospores. Single amino acid substitutions at positions 68 and 94 resulted in sigma factors that bind with less affinity to the core subunits of RNA polymerase. The substitution at position 68 did not affect the stability of the protein in B. subtilis; therefore, this substitution probably did not have large effects on the overall structure of the sigma factor. The substitution at position 68 probably defines a position in sigma E that closely contacts a subunit of RNA polymerase, while the substitution at position 94 may define a position that is important for protein stability or for binding to core RNA polymerase.

Characterization of cotJ, a sigma E-controlled operon affecting the polypeptide composition of the coat of Bacillus subtilis spores

The outermost protective structure found in endospores of Bacillus subtilis is a thick protein shell known as the coat, which makes a key contribution to the resistance properties of the mature spore and also plays a role in its interaction with compounds able to trigger germination. The coat is organized as a lamellar inner layer and an electron-dense outer layer and has a complex polypeptide composition. Here we report the cloning and characterization of an operon, cotJ, located at about 62 degrees on the B. subtilis genetic map, whose inactivation results in the production of spores with an altered pattern of coat polypeptides. The cotJ operon was identified by screening a random library of lacZ transcriptional fusions for a conditional (inducer-dependent) Lac+ phenotype in cells of a strain in which the structural gene (spoIIGB) for the early-acting, mother-cell-specific transcriptional factor sigma E was placed under the control of the IPTG (isopropyl-beta-D-thiogalactopyranoside)-inducible Pspac promoter. Sequence analysis of cloned DNA from the cotJ region complemented by genetic experiments revealed a tricistronic operon preceded by a strong sigma E-like promoter. Expression of an SP beta-borne cotJ-lacZ fusion commences at around h 2 of sporulation, as does expression of other sigma E-dependent genes, and shows an absolute requirement for sigma E. Studies with double-reporter strains bearing a cotJ-gusA fusion and lacZ fusions to other cot genes confirmed that expression of cotJ is initiated during sporulation prior to activation of genes known to encode coat structural proteins (with the sole exception of cotE). An in vitro-constructed insertion-deletion mutation in cotJ resulted in the formation of spores with no detectable morphological or resistance deficiency. However, examination of the profile of electrophoretically separated spore coat proteins from the null mutant revealed a pattern that was essentially identical to that of a wild-type strain in the range of 12 to 65 kDa, except for polypeptides of 17 and 24 kDa, the putative products of the second (cotJB) and third (cotJC) cistrons of the operon, that were missing or reduced in amount in the coat of the mutant. Polypeptides of the same apparent sizes are detected in spores of a cotE null mutant, on which basis we infer that the products of the cotJ operon are required for the normal formation of the inner layers of the coat or are themselves structural components of the coat. Because the onset of cotJ transcription is temporally coincident with the appearance of active sigma E, we speculate that the cotJ-encoded products may be involved in an early state of coat assembly.

Bacillus subtilis lon protease prevents inappropriate transcription of genes under the control of the sporulation transcription factor sigma G

The Bacillus subtilis RNA polymerase sigma factor sigma G is a cell-type-specific regulatory protein that governs the transcription of genes that are expressed at an intermediate to late stage of sporulation in the forespore compartment of the sporangium. Here we report the identification of a mutation (lon-1) that causes inappropriate transcription of genes under the control of sigma G under nutritional and genetic conditions in which sporulation is prevented. The mutation is located at 245 degrees on the genetic map and lies within a newly identified open reading frame that is predicted to encode a homolog to Lon protease. Inappropriate transcription of sigma G-controlled genes in the lon-1 mutant is not prevented by mutations in genes that are normally required for the appearance of sigma G during sporulation but is prevented by a mutation in the structural gene (spoIIIG) for sigma G itself. In light of previous work showing that spoIIIG is subject to positive autoregulation, we propose that Lon protease is responsible (possibly by causing degradation of sigma G) for preventing sigma G-directed transcription of spoIIIG and hence the accumulation of sigma G in cells that are not undergoing sporulation. An integrated physical and genetic map is presented that encompasses 36 kb of uninterrupted DNA sequence from the lon pheA region of the chromosome, corresponding to 245 degrees to 239 degrees on the genetic map.

Cloning and characterization of spoVR, a gene from Bacillus subtilis involved in spore cortex formation

Screening for sigma E-dependent promoters led to the isolation of a gene from Bacillus subtilis, designated spoVR, which appears to be involved in spore cortex formation. Cultures of strains carrying mutations in spoVR had an increased proportion of phase-dark spores, which correlated with an increased proportion of cortexless spores seen by electron microscopy. The numbers of heat- and chloroform-resistant phase-bright spores produced by these mutants were decreased by about 3- to 10-fold, and accumulation of dipicolinate was decreased by more than 3-fold. The spoVR gene was located on the B. subtilis chromosome immediately upstream from, and in the opposite orientation of, the phoAIV gene. Expression of spoVR was initiated at the second hour of sporulation from a sigma E-dependent promoter, and this expression did not require any of the other known mother-cell-specific transcriptional regulators. The spoVR gene was predicted to encode a product of 468 residues.

Subcellular localization of proteins involved in the assembly of the spore coat of Bacillus subtilis

Spores of the bacterium Bacillus subtilis are encased in a two-layered protein shell, which consists of an electron-translucent, lamellar inner coat, and an electron-dense outer coat. The coat protein CotE is both a structural component of the coat and a morphogenetic protein that is required for the assembly of the outer coat. We now show that CotE is located in the outer coat of the mature spore and that at an intermediate stage of sporulation, when the developing spore (the forespore) is present as a free protoplast within the sporangium, CotE is localized in a ring that surrounds the forespore but is separated from it by a small gap. We propose that the ring is the site of assembly of the outer coat and that the gap is the site of formation of the inner coat. Assembly of the ring depends on the sporulation protein SpoIVA, which sits close to or on the surface of the outer membrane that encircles the forespore. We propose that SpoIVA creates a basement layer around the forespore on which coat assembly takes place. The subcellular localization and assembly of CotE and other coat proteins are therefore determined by the capacity of SpoIVA to recognize and adhere to a specific surface within the sporangium, the outer membrane of the forespore.

Phosphorylation of Bacillus subtilis transcription factor Spo0A stimulates transcription from the spoIIG promoter by enhancing binding to weak 0A boxes

Activation of the spoIIG promoter at the onset of sporulation in Bacillus subtilis requires the regulatory protein, Spo0A, which binds to two sites in the promoter, sites 1 and 2. Phosphorylation of Spo0A is essential for the initiation of sporulation. Therefore, we examined the role of Spo0A phosphorylation in spoIIG promoter activation. Phosphorylation of Spo0A stimulated transcription from the spoIIG promoter in vitro. In DNAse I footprinting experiments with the spoIIG promoter, we found that phosphorylation of Spo0A increased its affinity for site 2 more than for site 1, which is the site to which nonphosphorylated Spo0A binds most avidly. This result could not be explained by increased cooperativity between Spo0A bound at sites 1 and 2 because the increased affinity for site 2 by phosphorylated Spo0A was also observed with a deletion derivative of the spoIIG promoter containing only site 2. We have located Spo0A-binding sequences in the spoIIG promoter by DMS protection assays and mutational analysis, and found that site 1 contains one higher-affinity binding sequence whereas site 2 contains two weaker-binding sites. Two substitutions in site 2 of the spoIIG promoter that change the sequence to be more like an optimal Spo0A-binding site were found to increase promoter activity. Moreover, phosphorylation of Spo0A was not required in vivo for activation of the spoIIG promoter containing these strong binding sites. The results suggest that the primary role for phosphorylation of Spo0A is to increase its affinity for specific sites rather than to activate an activity of Spo0A that acts on RNA polymerase at promoters.

Forespore-specific disappearance of the sigma-factor antagonist spoIIAB: implications for its role in determination of cell fate in Bacillus subtilis

Endospore formation in Bacillus subtilis is a morphologically complex process in which the bacterium divides into two compartments (forespore and mother cell) that follow different developmental paths. Compartment-specific transcription in the forespore is initiated by RNA polymerase containing sigma F, and results in the forespore-specific production of sigma G, which directs most of the subsequent forespore-specific transcription. The activity of sigma F is thought to be restricted to the forespore by the sigma factor antagonist SpoIIAB. We used antibodies against SpoIIAB to monitor its accumulation during sporulation. We found that SpoIIAB accumulates early after the initiation of sporulation, and that it was present in the mother-cell compartment 2h after sigma F became active in the forespore. SpoIIAB disappeared preferentially from the forespore during development, and its disappearance from the forespore compartment correlated with the activation of sigma G in that compartment, raising the possibility that SpoIIAB may be involved regulating sigma G activity. We tested whether SpoIIAB could antagonize sigma G activity by replacing the sigma F-dependent promoter that drives expression of spoIIIG, the structural gene for sigma G, with a sigma H-dependent promoter. This resulted in a lytic phenotype that was suppressed by the simultaneous expression of a plasmid-borne copy of spoIIAB. This suggests that SpoIIAB can suppress this effect of sigma G expression. Moreover, these cells formed spores efficiently.(ABSTRACT TRUNCATED AT 250 WORDS)

Cloning and characterization of a gene required for assembly of the Bacillus subtilis spore coat

During endospore formation in Bacillus subtilis, approximately a dozen proteins are synthesized and assembled around the prespore to form a protective coat. Little is known about the assembly process, but several of the genes encoding these coat proteins are expressed in the mother cell compartment, where the proteins accumulate on the outer side of the developing endospore. Transcription of these genes is directed by the mother cell-specific sigma factor, sigma K, during the later stages of endospore development. sigma E may direct expression of the genes that encode proteins that function in the earliest stages of coat assembly. By screening for sigma E-dependent promoters, we cloned a gene, designated spoVID, required for assembly of a normal spore coat. Expression of spoVID was initiated at about the second hour of sporulation and continued throughout development from a sigma E-dependent promoter. The spoVID gene was located on the B. subtilis chromosome just downstream of the previously characterized hemAXCDBL operon and is predicted to encode an extremely acidic protein with 575 residues. Insertion mutants of spoVID produced refractile spores that were resistant to heat and to chloroform but were sensitive to lysozyme. Electron microscopic examination of sporulating spoVID mutant cells revealed normal morphological development up to about the third hour of sporulation. However, during the later stages of development the coat proteins assembled into aberrant structures that occurred freely in the mother cell cytoplasm and that consisted of reiterations of the single inner and outer layers that normally make up the spore coat.

Genetic suppression analysis of sigma E interaction with three promoters in sporulating Bacillus subtilis

Genetic evidence suggests that the sigma (sigma) subunit of RNA polymerase determines the specificity of promoter utilization, by making sequence-specific contacts with DNA. We examined the effects of two single amino acid(aa) substitutions in sigma E on the utilization of mutated derivatives of three different promoters in sporulating Bacillus subtilis. We found allele-specific suppression of mutations in all three promoters by each aa substitution in sigma E. These results provide strong evidence that sigma E interacts with each of these promoters in vivo. Moreover, the specificity of suppression of the mutations by the aa substitutions in sigma E lead us to speculate that the Met124 of sigma E closely contacts two adjacent bp in the -10 region of the promoters.

Effects of amino acid substitutions in the -10 binding region of sigma E from Bacillus subtilis

The sigma subunit of bacterial RNA polymerase is required for specific binding to promoters. One region in most sigma factors makes sequence-specific contacts at the -10 region of its cognate promoters. To test the role of the amino acids in this -10 binding region, we examined the effects of 49 single-amino-acid substitutions in sigma E from Bacillus subtilis. We assayed the effect of each amino acid substitution on spore formation because sigma E is essential for endospore formation in B. subtilis. Our results showed that substitutions at several positions, including the highly conserved aromatic amino acid at position 102, had little or no detectable effect. Substitutions at another position, position 117, produced dominant negative mutations; we suggest that these mutations allow RNA polymerase containing the mutant sigma factor to bind specifically to promoters but prevent transcription initiation. Of the recessive defective alleles, those that produced substitutions at positions 113, 115, and 120 produced the most defective sigma factors. These results suggest that the residues at or near these positions in wild-type sigma E play important roles in sigma E function.

Spo0A controls the sigma A-dependent activation of Bacillus subtilis sporulation-specific transcription unit spoIIE

The spoIIE operon is a developmentally regulated transcription unit activated in the second hour of sporulation in Bacillus subtilis. Its promoter has an unusual structure, containing sequences which conform perfectly to the consensus for vegetative promoters recognized by sigma A-associated RNA polymerase (E sigma A), but with a spacing of 21 bp between the apparent -10 and -35 elements instead of the 17- or 18-bp spacing typical of promoters utilized by E sigma A. Mutations introduced into the apparent -10 element affected transcription in a manner consistent with its functioning as a polymerase recognition sequence. The deleterious effect of one -10 mutation was also suppressed in an allele-specific manner by a mutation in sigA known to suppress analogous -10 mutations in conventional vegetative promoters recognized by E sigma A. Similar suppression experiments failed to provide evidence for a direct interaction between E sigma A and the "-35-like" element, however, and DNase I protection experiments suggested instead that the Spo0A protein binds to a site overlapping this -35-like hexamer. Moreover, the effects of mutations within the -35-like hexamer on the binding of Spo0A in vitro paralleled their effects on transcription in vivo. We suggest that spoIIE belongs to a class of early-intermediate sporulation genes whose transcription by E sigma A is activated by the Spo0A protein.

Mutant sigma factor blocks transition between promoter binding and initiation of transcription

The sigma subunit of bacterial RNA polymerase is required for specific binding of the enzyme to promoters. This specificity is probably directed by two regions of most sigma factors that make sequence-specific contacts at two regions of promoters, the -10 and -35 regions. We found that a single amino acid substitution in the -10 recognition region of sigma E from Bacillus subtilis trapped RNA polymerase in a stable complex with promoter DNA in which it was unable to initiate transcription. Our results are consistent with the view that promoter utilization by RNA polymerase proceeds through several intermediate steps and suggest that the -10 recognition region of sigma factors may participate in a step that follows initial promoter binding.

Binding of Spo0A stimulates spoIIG promoter activity in Bacillus subtilis

The spoIIG promoter is used by RNA polymerase containing sigma A (E sigma A), the primary form of RNA polymerase found in vegetative cells in Bacillus subtilis. However, the spoIIG promoter is active only after the onset of sporulation. Activation of the spoIIG promoter requires the product of the spo0A gene (Spo0A). Spo0A is a sequence-specific DNA-binding protein which binds to two sites in the spoIIG promoter that are essential for promoter activity. We found that single-base-pair substitutions in these two regions that reduced promoter activity in vivo caused reduced binding of Spo0A in vitro, and one substitution that increased promoter activity in vivo increased the affinity of Spo0A for this DNA in vitro. Furthermore, Spo0A stimulated transcription from the spoIIG promoter by E sigma A in vitro. These results support the model that binding of Spo0A activates E sigma A-dependent transcription from the spoIIG promoter after the onset of sporulation.

Genetic evidence for interaction of sigma E with the spoIIID promoter in Bacillus subtilis

During sporulation in Bacillus subtilis, new RNA polymerase sigma factors are produced. These sigma factors direct the transcription of genes that are required for this cellular differentiation. In order to determine the role of each sigma factor in this process, it is necessary to know which promoters are recognized by each sigma factor. The spoIIID gene product plays an important role in the establishment of mother cell-specific gene expression during sporulation. We found that substitution of an alanine at position 124 of the sporulation-specific sigma factor sigma E suppressed the effect of a single-base-pair transition at position -13 of the spoIIID promoter. This alanine substitution in sigma E did not suppress the effect of a transversion at position -12 of the spoIIID promoter. The allele specificity of the interaction between sigma E and the spoIIID promoter is strong evidence that sigma E directs transcription from the spoIIID promoter during sporulation. Position 124 in sigma E is located within a region that is highly conserved among the regions in other sigma factors that probably interact with the -10 regions of their cognate promoters.

Deletion of spoIIAB blocks endospore formation in Bacillus subtilis at an early stage

During an early stage of endospore formation in Bacillus subtilis, the cell divides asymmetrically into two compartments that follow different developmental paths. The differential expression of genes in these two compartments is controlled in part by the production of compartment-specific transcription factors, sigma G and sigma K. It is not known how sigma G accumulation is restricted to one of the two compartments, the forespore. However, the observations that sigma F directs transcription of the structural gene for sigma G and that sigma F activity can be modified by the product of a gene, spoIIAB, has led us to investigate the role of spoIIAB during sporulation. We have isolated mutants that carry deletion alleles of spoIIAB. Electron microscopic examination of these mutants revealed that these mutations blocked endospore formation at an early stage before septation and caused extensive cell lysis. The spoIIAB deletion alleles caused hyperexpression of genes that are normally expressed exclusively in the forespore compartments of sporulating wild-type cells, whereas these alleles reduced expression of other genes, including spoIIE, which is expressed before septation in wild-type cells. These observations confirm that spoIIAB is essential for sporulation and are consistent with models in which the product of spoIIAB plays a role in regulating the timing and/or compartment specificity of sigma F- and sigma G-directed transcription.

Expression of stage II genes during sporulation in Bacillus subtilis

Two RNA polymerase sigma factors, sigma F and sigma E, are produced during the first two hours of endospore formation in Bacillus subtilis. Transcription of the structural genes for these factors is activated about one hour after the start of endospore formation. The operon encoding sigma F is transcribed by RNA polymerase containing sigma H, another secondary sigma factor, whereas the operon encoding sigma E is transcribed by RNA polymerase containing sigma A, the primary sigma factor in growing cells. Evidently, the coordinate temporal control of these transcriptional units is mediated by a factor other than the sigma factors, possibly by the DNA-binding protein encoded by spo0A. Both sigma F and sigma E activities are also regulated by mechanisms operating after transcription.

Genetic evidence for interaction of sigma A with two promoters in Bacillus subtilis

The specificity of promoter binding by RNA polymerase is governed by the sigma subunit. Recent studies, in which single-amino-acid substitutions in sigma factors have been found to suppress the effects of specific base pair substitutions in promoters, support the model that these sigma factors make sequence-specific contacts with nucleotides at the -10 and -35 regions of promoters. We found that single-amino-acid substitutions in the putative -35 region and -10 region recognition domains of sigma A specifically suppressed the effects of mutations in the -35 and -10 regions, respectively, of two promoters that are expressed in exponentially growing Bacillus subtilis. These mutations change the specificity of sigma A, the primary sigma factor in growing B. subtilis, and demonstrate that this sigma factor interacts with promoters in a manner similar to that of its homolog in Escherichia coli, sigma 70. These mutant derivatives of sigma A also provide a tool that may be useful for determining whether sigma A uses specific promoters in vivo.

Spo0A binds to a promoter used by sigma A RNA polymerase during sporulation in Bacillus subtilis

Examination of the effects of 56 single-base-pair substitutions in the spoIIG promoter and studies of the interaction of the spo0A product (Spo0A) with this promoter in vitro demonstrated that Spo0A acts directly to enable this promoter to be used by sigma A-associated RNA polymerase (EC 2.7.7.6). The spoIIG operon from Bacillus subtilis is transcribed during sporulation by a form o RNA polymerase containing sigma A, the primary sigma factor in vegetative cells. The spoIIG promoter is unusual in that it contains sequences that are similar to those found at the -10 and -35 regions of promoters that are used by sigma A-associated RNA polymerase, but these sigma A-like recognition sequences are separated by 22 base pairs rather than the typical 17 or 18 base pairs. We found that single-base-pair substitutions in the around the -35-like sequence, and substitutions in a region upstream from this position, around position -87, reduced promoter activity. DNase I protection and electrophoretic gel mobility shift assays were used to demonstrate that Spo0A binds specifically to these regions in vitro. Evidently, the -35-like sequence is part of a Spo0A binding site and therefore is possibly not a sigma A-recognition sequence. These results support a model in which Spo0A activates the spoIIG promoter after the onset of endospore formation.

Transcription of the Bacillus subtilis spoIIA locus

The spoIIA operon encodes three genes, including the structural gene for a sporulation-induced sigma factor sigma F. We used deletion analysis of spoIIA-lacZ fusions to define the location of the spoIIA promoter. We found that sigma H-RNA polymerase transcribes spoIIA accurately in vitro and propose that sigma H directs transcription of spoIIA during sporulation.

Control of developmental transcription factor sigma F by sporulation regulatory proteins SpoIIAA and SpoIIAB in Bacillus subtilis

The sporulation operon spoIIA of Bacillus subtilis consists of three cistrons called spoIIAA, spoIIAB, and spoIIAC. Little is known about the function of spoIIAA and spoIIAB, but spoIIAC encodes a sigma factor called sigma F, which is capable of directing the transcription in vitro of genes that are expressed in the forespore chamber of the developing sporangium. We now report that the products of the spoIIA operon constitute a regulatory system in which SpoIIAA is an antagonist of SpoIIAB (or otherwise counteracts the effect of SpoIIAB) and SpoIIAB is, in turn, an antagonist of SpoIIAC (sigma F). This conclusion is based on the observations that (i) overexpression of spoIIAB inhibits sigma F-directed gene expression, (ii) a mutation in spoIIAB stimulates sigma F-directed gene expression, (iii) a mutation in spoIIAA blocks sigma F-directed gene expression, and (iv) a mutation in spoIIAB relieves the block in sigma F-directed gene expression caused by a mutation in spoIIAA. The SpoIIAA/SpoIIAB/SpoIIAC regulatory system could play a role in controlling the timing of sigma F-directed gene expression and/or could be responsible for restricting sigma F-directed gene expression to the forespore chamber of the sporangium.