Expression of the gene encoding glycerol-3-phosphate dehydrogenase (glpD) in Bacillus subtilis is controlled by antitermination

Development of a Glycerol-Inducible Expression System for High-Yield Heterologous Protein Production in Bacillus subtilis

The development of efficient, low-cost, and robust expression systems is important for the mass production of proteins and natural products in large amounts using cell factories. Glycerol is an ideal carbon source for large-scale fermentation due to its low cost and favorable maintenance of the fermentation process. Here, we used the antiterminator protein GlpP and its target promoter P_glpD to construct a highly efficient glycerol-inducible expression system (GIES) in Bacillus subtilis. This system was able to express heterologous genes in an autoinducible manner based on the sequential utilization of glucose and glycerol under the regulation of carbon catabolite repression. In such a system, the concentration of glycerol regulated the strength of gene expression, and the concentration of glucose affected both the timing of induction and the strength of gene expression. By enhancing GlpP, the GIES was further strengthened for high-level intracellular expression of aspartase and secretory expression of nattokinase. High yields of nattokinase in a 5-L fermenter through batch and fed-batch fermentation demonstrated the potential to apply the GIES for large-scale enzyme production. Through the evolution of the -10 box of P_glpD, mutants with gradient activities were obtained. In addition, hybrid glycerol-inducible promoters were successfully constructed by combining the constitutive promoters and the 5' untranslated region of P_glpD. Collectively, this study developed a GIES to obtain high-value products from inexpensive glycerol. More importantly, the great potential of the pair of inherent terminator and antiterminator protein as a portable biological tool for various purposes in synthetic biology is proposed. IMPORTANCE In this study, a GIES was constructed in B. subtilis by employing the antiterminator protein GlpP and the GlpP-regulated promoter P_glpD. Based on the sequential utilization of glucose and glycerol by B. subtilis, the GIES was able to express genes in an autoinducible manner. The amounts and ratio of glucose and glycerol can regulate the gene induction timing and expression strength. The GIES was further applied for high yields of nattokinase, and its robustness in production scale-up was confirmed in a 5-L fermenter. The high-level expression of heterologous proteins demonstrated the huge application potential of the GIES. Furthermore, mutants of P_glpD with gradient activities and hybrid glycerol-inducible promoters were obtained through the evolution of the -10 box of P_glpD and the combination of the constitutive promoters and the 5' untranslated region of P_glpD, respectively. These results demonstrated the use of the antiterminator protein as a regulator for various purposes in synthetic biology.

A Novel Function of δ Factor from Bacillus subtilis as a Transcriptional Repressor

δ, a small protein found in most Gram-positive bacteria was, for a long time, thought to be a subunit of RNA polymerase (RNAP) and was shown to be involved in recycling of RNAP at the end of each round of transcription. However, how δ participates in both up-regulation and down-regulation of genes in vivo remains unclear. We have recently shown, in addition to the recycling of RNAP, δ functions as a transcriptional activator by binding to an A-rich sequence located immediately upstream of the -35 element, consequently facilitating the open complex formation. The result had explained the mechanism of up-regulation of the genes by δ. Here, we show that Bacillus subtilis δ could also function as a transcriptional repressor. Our results demonstrate that δ binds to an A-rich sequence located near the -35 element of the spo0B promoter, the gene involved in the regulatory cascade of bacterial sporulation and inhibits the open complex formation due to steric clash with σ region 4.2. We observed a significant increase in the mRNA level of the spo0B gene in a δ-knock-out strain of B. subtilis compared with the wild-type. Thus, the results report a novel function of δ, and suggest the mechanism of down-regulation of genes in vivo by the protein.

Characterization of HelD, an interacting partner of RNA polymerase from Bacillus subtilis

Bacterial RNA polymerase (RNAP) is an essential multisubunit protein complex required for gene expression. Here, we characterize YvgS (HelD) from Bacillus subtilis, a novel binding partner of RNAP. We show that HelD interacts with RNAP-core between the secondary channel of RNAP and the alpha subunits. Importantly, we demonstrate that HelD stimulates transcription in an ATP-dependent manner by enhancing transcriptional cycling and elongation. We demonstrate that the stimulatory effect of HelD can be amplified by a small subunit of RNAP, delta. In vivo, HelD is not essential but it is required for timely adaptations of the cell to changing environment. In summary, this study establishes HelD as a valid component of the bacterial transcription machinery.

How phosphotransferase system-related protein phosphorylation regulates carbohydrate metabolism in bacteria

The phosphoenolpyruvate(PEP):carbohydrate phosphotransferase system (PTS) is found only in bacteria, where it catalyzes the transport and phosphorylation of numerous monosaccharides, disaccharides, amino sugars, polyols, and other sugar derivatives. To carry out its catalytic function in sugar transport and phosphorylation, the PTS uses PEP as an energy source and phosphoryl donor. The phosphoryl group of PEP is usually transferred via four distinct proteins (domains) to the transported sugar bound to the respective membrane component(s) (EIIC and EIID) of the PTS. The organization of the PTS as a four-step phosphoryl transfer system, in which all P derivatives exhibit similar energy (phosphorylation occurs at histidyl or cysteyl residues), is surprising, as a single protein (or domain) coupling energy transfer and sugar phosphorylation would be sufficient for PTS function. A possible explanation for the complexity of the PTS was provided by the discovery that the PTS also carries out numerous regulatory functions. Depending on their phosphorylation state, the four proteins (domains) forming the PTS phosphorylation cascade (EI, HPr, EIIA, and EIIB) can phosphorylate or interact with numerous non-PTS proteins and thereby regulate their activity. In addition, in certain bacteria, one of the PTS components (HPr) is phosphorylated by ATP at a seryl residue, which increases the complexity of PTS-mediated regulation. In this review, we try to summarize the known protein phosphorylation-related regulatory functions of the PTS. As we shall see, the PTS regulation network not only controls carbohydrate uptake and metabolism but also interferes with the utilization of nitrogen and phosphorus and the virulence of certain pathogens.

RNA processing and degradation in Bacillus subtilis

This review focuses on the enzymes and pathways of RNA processing and degradation in Bacillus subtilis, and compares them to those of its gram-negative counterpart, Escherichia coli. A comparison of the genomes from the two organisms reveals that B. subtilis has a very different selection of RNases available for RNA maturation. Of 17 characterized ribonuclease activities thus far identified in E. coli and B. subtilis, only 6 are shared, 3 exoribonucleases and 3 endoribonucleases. Some enzymes essential for cell viability in E. coli, such as RNase E and oligoribonuclease, do not have homologs in B. subtilis, and of those enzymes in common, some combinations are essential in one organism but not in the other. The degradation pathways and transcript half-lives have been examined to various degrees for a dozen or so B. subtilis mRNAs. The determinants of mRNA stability have been characterized for a number of these and point to a fundamentally different process in the initiation of mRNA decay. While RNase E binds to the 5' end and catalyzes the rate-limiting cleavage of the majority of E. coli RNAs by looping to internal sites, the equivalent nuclease in B. subtilis, although not yet identified, is predicted to scan or track from the 5' end. RNase E can also access cleavage sites directly, albeit less efficiently, while the enzyme responsible for initiating the decay of B. subtilis mRNAs appears incapable of direct entry. Thus, unlike E. coli, RNAs possessing stable secondary structures or sites for protein or ribosome binding near the 5' end can have very long half-lives even if the RNA is not protected by translation.

Antitermination by GlpP, catabolite repression via CcpA and inducer exclusion triggered by P-GlpK dephosphorylation control Bacillus subtilis glpFK expression

The Bacillus subtilis glpFK operon encoding the glycerol transport facilitator (GlpF) and glycerol kinase (GlpK) is induced by glycerol-3-P and repressed by rapidly metabolizable sugars. Carbon catabolite repression (CCR) of glpFK is partly mediated via a catabolite response element cre preceding glpFK. This operator site is recognized by the catabolite control protein A (CcpA) in complex with one of its co-repressors, P-Ser-HPr or P-Ser-Crh. HPr is a component of the phosphoenolpyruvate:sugar phosphotransferase system (PTS), and Crh is an HPr homologue. The hprK-encoded HPr kinase phosphorylates HPr and Crh at Ser-46. But in neither ccpA nor hprK mutants was expression of a glpF'-lacZ fusion relieved from CCR, as a second, CcpA-independent CCR mechanism implying the terminator tglpFK, whose formation is prevented by the glycerol-3-P-activated antiterminator GlpP, is operative. Deletion of tglpFK led to elevated expression of the glpF'-lacZ fusion and to partial relief from CCR. CCR completely disappeared in DeltatglpFK mutants carrying a disruption of ccpA or hprK. The tglpFK-requiring CCR mechanism seems to be based on insufficient synthesis of glycerol-3-P, as CCR of glpFK was absent in ccpA mutants growing on glycerol-3-P or synthesizing H230R mutant GlpK. In cells growing on glycerol, glucose prevents the phosphorylation of GlpK by P-His-HPr. P-GlpK is much more active than GlpK, and the absence of P~GlpK formation in DeltaptsHI strains prevents glycerol metabolism. As a consequence, only small amounts of glycerol-3-P will be formed in glycerol and glucose-exposed cells (inducer exclusion). The uptake of glycerol-3-P via GlpT provides high concentrations of this metabolite in the ccpA mutant and allows the expression of the glpF'-lacZ fusion even when glucose is present. Similarly, despite the presence of glucose, large amounts of glycerol-3-P are formed in a glycerol-exposed strain synthesizing GlpKH230R, as this mutant GlpK is as active as P-GlpK.

Different processing of an mRNA species in Bacillus subtilis and Escherichia coli

Expression of the Bacillus subtilis glpD gene, which encodes glycerol-3-phosphate (G3P) dehydrogenase, is controlled by termination or antitermination of transcription. The untranslated leader sequence of glpD contains an inverted repeat that gives rise to a transcription terminator. In the presence of G3P, the antiterminator protein GlpP binds to glpD leader mRNA and promotes readthrough of the terminator. Certain mutations in the inverted repeat of the glpD leader result in GlpP-independent, temperature-sensitive (TS) expression of glpD. The TS phenotype is due to temperature-dependent degradation of the glpD mRNA. In the presence of GlpP, the glpD mRNA is stabilized. glpD leader-lacZ fusions were integrated into the chromosomes of B. subtilis and Escherichia coli. Determination of steady-state levels of fusion mRNA in B. subtilis showed that the stability of the fusion mRNA is determined by the glpD leader part. Comparison of steady-state levels and half-lives of glpD leader-lacZ fusion mRNA in B. subtilis and E. coli revealed significant differences. A glpD leader-lacZ fusion transcript that was unstable in B. subtilis was considerably more stable in E. coli. GlpP, which stabilizes the transcript in B. subtilis, did not affect its stability in E. coli. Primer extension analysis showed that the glpD leader-lacZ fusion transcript is processed differently in B. subtilis and in E. coli. The dominating cleavage site in E. coli was barely detectable in B. subtilis. This site was shown to be a target of E. coli RNase III.

Catabolite regulation of the Bacillus subtilis ctaBCDEF gene cluster

Bacillus subtilis cytochrome c oxidase caa3 is encoded by the ctaCDEF genes at the ctaABCDEF locus, with the ctaBCDEF genes organized as an operon-like unit. A dyad symmetry sequence and a catabolite response element homolog can be recognized in the 240-bp intercistronic region between ctaB and ctaC. ctaB'-lacZ and ctaBCD'-lacZ transcriptional fusions integrated at the native locus were used to study catabolite effects on transcription of the ctaB and ctaCDEF genes. In Schaeffer's medium lacking glucose, ctaBCD'-lacZ was expressed at a very low level during the exponential phase, and expression increased about 30-fold 2 h after entry into the stationary phase. In the presence of 0.5% glucose, ctaBCD'-lacZ expression was totally repressed. In contrast to ctaBCD'-lacZ, ctaB'-lacZ was constitutively expressed regardless of carbon source. The ctaCDEF genes were separated from ctaB by insertion of plasmids carrying selectable markers in such a way that the ctaCDEF and ctaB transcription units remained intact. Enzymatic assays of caa3 with these constructs, showed that ctaCDEF was not expressed independently of ctaB. Also, when a 'ctaB-ctaC'-lacZ fusion (containing the ctaB-ctaC intercistronic region) was placed at a remote nonessential locus, beta-galactosidase activity could not be detected. The absence of a promoter in the ctaB-ctaC intercistronic space also was indicated by the inability to detect ctaC-specific transcripts with RNase protection assays, primer extension, and rapid amplification of 5' cDNA ends. Direct mRNA measurements showed that, in the presence of 0.5% glucose, ctaBCDEF transcripts terminated at the 3' end of the putative stem-loop structure and the distal portion was down-regulated. A possible mechanism for ctaCDEF gene regulation is suggested. Catabolite repression of ctaBCD'-lacZ was partly dependent on CcpA but was independent of HPr. The expression of ctaBCDEF also appears to require the strC, ctaA, and resD-resE gene products.

The Bacillus subtilis glpD leader and antiterminator protein GlpP provide a target for glucose repression in Escherichia coli

Expression of the Bacillus subtilis glpD gene which encodes glycerol-3-phosphate (G3P) dehydrogenase is regulated by the GlpP protein which, in the presence of G3P, causes antitermination of transcription of glpD. The glpD gene leader fused to lacZ was integrated into the chromosome of Escherichia coli deleted for the lac operon and carrying the B. subtilis glpP gene on a plasmid. beta-Galactosidase activity of this strain was increased by the addition of G3P. When G3P and glucose, glucose-6-phosphate or fructose-6-phosphate were added, beta-galactosidase activity was reduced showing that GlpP mediates catabolite repression of transcription from the glpD leader in the absence of any other B. subtilis protein.

Antiterminator protein GlpP of Bacillus subtilis binds to glpD leader mRNA

The Bacillus subtilis glpD gene encodes glycerol-3-phosphate (G3P) dehydrogenase. Expression of glpD is mainly controlled by termination/antitermination of transcription at an inverted repeat in the glpD leader. Antitermination is mediated by the antiterminator protein GlpP in the presence of G3P. In this paper, interaction between GlpP and glpD leader mRNA in vivo and in vitro is reported. In vivo, the antiterminating effect of GlpP can be titrated in a strain carrying the glpD leader on a plasmid. GlpP has been purified and gel shift experiments have shown that it binds to glpD leader mRNA in vitro. GlpP is not similar to other known antiterminator proteins, but database searches have revealed an Escherichia coli ORF which has a high degree of similarity to GlpP.

LicT, a Bacillus subtilis transcriptional antiterminator protein of the BglG family

Gene licS of Bacillus subtilis encodes an excreted Beta-1,3-1,4-endoglucanase necessary for lichenan utilization. Upstream of licS we found a gene (termed licT) together with its promoter which encodes a transcriptional antiterminator of the BglG family. Genes licT and licS are separated by a palindromic sequence (lic-t) reminiscent of transcriptional terminators recognized by the antiterminator proteins of the BglG family. The LicT protein can prevent termination at terminator lic-t and also at terminator t2 of the Escherichia coli bgl operon and BglG prevents termination at lic-t. The role of LicT in licS regulation by preventing termination at its terminator lic-t appears to be limited since expression of licS is inducible only two- to threefold. This limited regulation is mainly due to a high basal level of licS expression which can in part be attributed to the presence of a second promoter preceding licS and located downstream of lic-t. However, disruption of gene licT leads not only to loss of inducibility of licS but also to loss of growth on lichenan or on its degradation products, indicating its stringent role in beta-glucan utilization.

Aminoacyl-tRNA synthetase gene regulation in Bacillus subtilis

In this review, we summarize progress on the regulation of the aminoacyl-tRNA synthetase genes in Bacillus subtilis. Most of the genes encoding this set of enzymes in B subtilis are members of a large family of Gram-positive genes and operons controlled by a novel antitermination mechanism that uses their cognate uncharged tRNA as the effector. A subset of these genes is, in addition, likely to be controlled at the level of mRNA processing and degradation. We describe the key experiments leading to these conclusions.

Compilation and analysis of Bacillus subtilis sigma A-dependent promoter sequences: evidence for extended contact between RNA polymerase and upstream promoter DNA

Sequence analysis of 236 promoters recognized by the Bacillus subtilis sigma A-RNA polymerase reveals an extended promoter structure. The most highly conserved bases include the -35 and -10 hexanucleotide core elements and a TG dinucleotide at position -15, -14. In addition, several weakly conserved A and T residues are present upstream of the -35 region. Analysis of dinucleotide composition reveals A2- and T2-rich sequences in the upstream promoter region (-36 to -70) which are phased with the DNA helix: An tracts are common near -43, -54 and -65; Tn tracts predominate at the intervening positions. When compared with larger regions of the genome, upstream promoter regions have an excess of An and Tn sequences for n > 4. These data indicate that an RNA polymerase binding site affects DNA sequence as far upstream as -70. This sequence conservation is discussed in light of recent evidence that the alpha subunits of the polymerase core bind DNA and that the promoter may wrap around RNA polymerase.

Mutations in the glycerol kinase gene restore the ability of a ptsGHI mutant of Bacillus subtilis to grow on glycerol

Although glycerol is not taken up via the phosphotransferase system (PTS) in Bacillus subtilis, some mutations that affect the general components of the PTS impair the ability of cells to grow on glycerol. Five revertants of a pts deletion mutant that grow on glycerol were analysed. They were shown to carry mutations in the glycerol kinase gene. These are missense mutations located in parts of the glpK gene that could encode regions important for the activity of glycerol kinase. The results strongly suggest that the main effect of the PTS on glycerol utilization in B. subtilis is mediated via glycerol kinase.

Roles of the three transcriptional attenuators of the Bacillus subtilis pyrimidine biosynthetic operon in the regulation of its expression

Expression of the Bacillus subtilis pyr operon is regulated by exogenous pyrimidines and the protein product of the first gene of the operon, PyrR. It has been proposed that PyrR mediates transcriptional attenuation at three untranslated segments of the operon (R.J. Turner, Y. Lu, and R.L. Switzer, J. Bacteriol., 176:3708-3722, 1994). In this study, transcriptional fusions of the pyr promoter followed by the pyr attenuation sequences, either individually or in tandem to a lacZ reporter gene, were used to examine the physiological functions of all three attenuators through their ability to affect beta-galactosidase expression. These fusions were studied as chromosomal integrants in various B. subtilis strains to examine the entire range of control by pyrimidines, PyrR dependence, amd developmental control of pyr gene expression. The nutritional regulation of each attenuator separately was roughly equivalent to that of the other two and was totally dependent upon PyrR, and that of tandem attenuators was cumulative. The regulation of a fusion of the spac promoter followed by the pyrP:pyrB intercistronic region to lacZ produced results similar to those obtained with the corresponding fusion containing the pyr promoter, demonstrating that attenuator-dependent regulation is independent of the promoter. Extreme pyrimidine starvation gave rise to two- to threefold-higher levels of expression of a pyr-lacZ fusion that lacked attenuators, independent of PyrR, than were obtained with cells that were not starved. Increased expression of a similar spac-lacZ fusion during pyrimidine starvation was also observed, however, indicating that attenuator-independent regulation is not a specific property of the pyr operon. Conversion of the initiator AUG codon in a small open reading frame in the pyrP:pyrB intercistronic region to UAG reduced expression by about half but did not alter regulation by pyrimidines, which excludes the possibility of a coupled transcription-translation attenuation mechanism. Developmental regulation of pyr expression during early stationary phase was found to be dependent upon the attenuators and PyrR, and the participation of SpoOA was excluded.

Bacillus subtilis CtaA is a heme-containing membrane protein involved in heme A biosynthesis

Heme A is a prosthetic group of many respiratory oxidases. It is synthesized from protoheme IX (heme B) seemingly with heme O as a stable intermediate. The Bacillus subtilis ctaA and ctaB genes are required for heme A and heme O synthesis, respectively (B. Svensson, M. Lübben, and L. Hederstedt, Mol. Microbiol. 10:193-201, 1993). Tentatively, CtaA is involved in the monooxygenation and oxidation of the methyl side group on porphyrin ring D in heme A synthesis from heme B. B. subtilis ctaA and ctaB on plasmids in both B. subtilis and Escherichia coli were found to result in a novel membrane-bound heme-containing protein with the characteristics of a low-spin b-type cytochrome. It can be reduced via the respiratory chain, and in the reduced state it shows light absorption maxima at 428, 528, and 558 nm and the alpha-band is split. Purified cytochrome isolated from both B. subtilis and E. coli membranes contained one polypeptide identified as CtaA by amino acid sequence analysis, about 0.2 mol of heme B per mol of polypeptide, and small amounts of heme A.

Analysis of a cis-active sequence mediating catabolite repression in gram-positive bacteria

One form of catabolite repression (CR) in the Gram-positive genus, Bacillus, is mediated by a cis-acting element (CRE). We use here a consensus sequence to identify such elements in sequenced genes of Gram-positive bacteria. These are analysed with respect to position and type of gene in which they occur. CRE sequences near the promoter region are mainly identified in genes encoding carbon catabolic enzymes, which are thus likely to be subject to CR by a global mechanism. Functional aspects of CREs are evaluated.

Regulation of glycerol metabolism in Enterococcus faecalis by phosphoenolpyruvate-dependent phosphorylation of glycerol kinase catalyzed by enzyme I and HPr of the phosphotransferase system

Using a polyclonal antibody against glycerol kinase from Enterococcus faecalis, we could demonstrate that glycerol kinase is inducible by growth on glycerol-containing medium and that during growth on glycerol the enzyme is mainly phosphorylated. Glucose and other sugars metabolized via the Embden-Meyerhof pathway strongly repressed the synthesis of glycerol kinase, while if glycerol was also present during growth, low activity, reflecting partial induction and the presence of mainly unphosphorylated, less active enzyme, was found. With gluconate, which is also a substrate of the phosphotransferase system, repression of glycerol kinase was less severe, but the enzyme was mainly present in the less active, unphosphorylated form. Effects of growth on different carbon sources on glycerol uptake are also reported.

Reconstitution of Bacillus subtilis trp attenuation in vitro with TRAP, the trp RNA-binding attenuation protein

We have reconstituted Bacillus subtilis trp attenuation in vitro. Purification of the mtrB gene product (TRAP) to near homogeneity allowed us to demonstrate that addition of this protein plus L-tryptophan to template, RNA polymerase, and nucleoside triphosphates caused transcription termination in the trpEDCFBA leader region. TRAP acts by binding to the nascent transcript and preventing formation of an RNA antiterminator structure, thereby allowing terminator formation and transcription termination. Oligonucleotides complementary to segments of the antiterminator were used to demonstrate that formation of this RNA hairpin was responsible for transcription read-through. TRAP was found to be a 60-kDa multimeric protein composed of identical 6- to 8-kDa subunits, and its elution profile on a chromatographic column did not change in the presence of tryptophan.

The role of phosphorylation of HPr, a phosphocarrier protein of the phosphotransferase system, in the regulation of carbon metabolism in gram-positive bacteria

HPr of the Gram-positive bacterial phosphotransferase system (PTS) can be phosphorylated by an ATP-dependent protein kinase on a serine residue or by PEP-dependent Enzyme 1 on a histidyl residue. Both phosphorylation events appear to influence the metabolism of non-PTS carbon sources. Catabolite repression of the gluconate (gnt) operon of B. subtilis appears to be regulated by the former phosphorylation event, while glycerol kinase appears to be regulated by the latter phosphorylation reaction. The extent of our understanding of these processes will be described.

Utilisation of glycerol and glycerol 3-phosphate is differently affected by the phosphotransferase system in Bacillus subtilis

Glycerol and glycerol 3-phosphate uptake in Bacillus subtilis does not involve the phosphotransferase system. In spite of this, B. subtilis mutants defective in the general components of the phosphotransferase system, EnzymeI or Hpr, are unable to grow with glycerol as sole carbon and energy source. Here we show that a Hpr mutant can grow on glycerol 3-phosphate and that glycerol 3-phosphate, but not glycerol, can induce glpD encoding glycerol-3-phosphate dehydrogenase. Induction of glpD also requires the glpP gene product which is a regulator of all known glp genes. Thus the phosphotransferase system general components do not interfere with the overall regulation of the glp regulon. Revertants of a Hpr mutant which can grown on glycerol carry mutations closely linked to the glp region at 75 degrees on the B. subtilis chromosomal map. This region contains the glpP, the glpFK and the glpD operons. The glpFK operon encodes the glycerol uptake facilitator (glpF) and glycerol kinase (glpK). The present results demonstrate that one of these genes, or their gene products, is the target for phosphotransferase system control of glycerol utilisation. Furthermore we conclude that utilisation of glycerol and glycerol 3-phosphate is differently affected by the phosphotransferase system in B. subtilis.

An inverted repeat preceding the Bacillus subtilis glpD gene is a conditional terminator of transcription

The Bacillus subtilis glpD gene, encoding glycerol-3-phosphate (G3P) dehydrogenase, is preceded by a promoter and an inverted repeat which is located between the promoter and the glpD coding region. The inverted repeat acts as a transcriptional terminator in vitro. Expression of glpD is induced by G3P in the presence of the glpP gene product. Full-length glpD transcripts can be detected only in glycerol-induced cells. The major glpD transcript is initiated from the glpD promoter but minor amounts of larger transcripts, possibly initiated at upstream glp promoters, can also be found. In uninduced cells short transcripts are present, corresponding to initiation at the glpD promoter and termination at the inverted repeat. Upon induction, these short transcripts disappear and are replaced by full-length glpD transcripts. The 3'-ends of full-length glpD transcripts were mapped to an inverted repeat located immediately downstream of glpD. These results show that glpD of B. subtilis is regulated by termination/antitermination of transcription.