phs Locus of Escherichia coli, a mutation causing pleiotropic lesions in metabolism, is an rpoA allele

The critical role of S-lactoylglutathione formation during methylglyoxal detoxification in Escherichia coli

Survival of exposure to methylglyoxal (MG) in Gram-negative pathogens is largely dependent upon the operation of the glutathione-dependent glyoxalase system, consisting of two enzymes, GlxI (gloA) and GlxII (gloB). In addition, the activation of the KefGB potassium efflux system is maintained closed by glutathione (GSH) and is activated by S-lactoylGSH (SLG), the intermediate formed by GlxI and destroyed by GlxII. Escherichia coli mutants lacking GlxI are known to be extremely sensitive to MG. In this study we demonstrate that a ΔgloB mutant is as tolerant of MG as the parent, despite having the same degree of inhibition of MG detoxification as a ΔgloA strain. Increased expression of GlxII from a multicopy plasmid sensitizes E. coli to MG. Measurement of SLG pools, KefGB activity and cytoplasmic pH shows these parameters to be linked and to be very sensitive to changes in the activity of GlxI and GlxII. The SLG pool determines the activity of KefGB and the degree of acidification of the cytoplasm, which is a major determinant of the sensitivity to electrophiles. The data are discussed in terms of how cell fate is determined by the relative abundance of the enzymes and KefGB.

Linkage map of Escherichia coli K-12, edition 10: the traditional map

This map is an update of the edition 9 map by Berlyn et al. (M. K. B. Berlyn, K. B. Low, and K. E. Rudd, p. 1715-1902, in F. C. Neidhardt et al., ed., Escherichia coli and Salmonella: cellular and molecular biology, 2nd ed., vol. 2, 1996). It uses coordinates established by the completed sequence, expressed as 100 minutes for the entire circular map, and adds new genes discovered and established since 1996 and eliminates those shown to correspond to other known genes. The latter are included as synonyms. An alphabetical list of genes showing map location, synonyms, the protein or RNA product of the gene, phenotypes of mutants, and reference citations is provided. In addition to genes known to correspond to gene sequences, other genes, often older, that are described by phenotype and older mapping techniques and that have not been correlated with sequences are included.

Mutations affecting two adjacent amino acid residues in the alpha subunit of RNA polymerase block transcriptional activation by the bacteriophage P2 Ogr protein

The bacteriophage P2 ogr gene product is a positive regulator of transcription from P2 late promoters. The ogr gene was originally defined by compensatory mutations that overcame the block to P2 growth imposed by a host mutation, rpoA109, in the gene encoding the alpha subunit of RNA polymerase. DNA sequence analysis has confirmed that this mutation affects the C-terminal region of the alpha subunit, changing a leucine residue at position 290 to a histidine (rpoAL290H). We have employed a reporter plasmid system to screen other, previously described, rpoA mutants for effects on activation of a P2 late promoter and have identified a second allele, rpoA155, that blocks P2 late transcription. This mutation lies just upstream of rpoAL290H, changing the leucine residue at position 289 to a phenylalanine (rpoAL289F). The effect of the rpoAL289F mutation is not suppressed by the rpoAL290H-compensatory P2 ogr mutation. P2 ogr mutants that overcome the block imposed by rpoAL289F were isolated and characterized. Our results are consistent with a direct interaction between Ogr and the alpha subunit of RNA polymerase and support a model in which transcription factor contact sites within the C terminus of alpha are discrete and tightly clustered.

Effects of rpoA and cysB mutations on acid induction of biodegradative arginine decarboxylase in Escherichia coli

For Escherichia coli, there have been more and more examples illustrating that the alpha subunit of RNA polymerase is directly involved in the activation of gene transcription by interaction with activator proteins. Because of the vital function of the alpha subunit in cell growth, only a limited number of mutations in its structural gene, rpoA, have been isolated. We obtained a number of these mutants and examined the effects of these mutations on the acid induction of adi and cad gene expression. Several mutations caused a small reduction in adi promoter activity at inducing pH. One mutation, rpoA341, essentially eliminated adi promoter activity, while it had little effect on the cad promoter. During the course of a separate study, we isolated a plasmid that enhanced adi expression. Further characterization of this plasmid showed that it contained cysB, the structural gene for the positive regulator for most cys operon genes. Introduction of a cysB mutation into an adi::lac fusion strain and beta-galactosidase assay studies of the resultant adi::lac cysB mutant established that a wild-type cysB gene was required for efficient acid induction of adi expression. These results suggest that a possible interaction between CysB and the alpha subunit of RNA polymerase is involved in activation of adi transcription.

Mechanisms of genome propagation and helper exploitation by satellite phage P4

Temperate coliphage P2 and satellite phage P4 have icosahedral capsids and contractile tails with side tail fibers. Because P4 requires all the capsid, tail, and lysis genes (late genes) of P2, the genomes of these phages are in constant communication during P4 development. The P4 genome (11,624 bp) and the P2 genome (33.8 kb) share homologous cos sites of 55 bp which are essential for generating 19-bp cohesive ends but are otherwise dissimilar. P4 turns on the expression of helper phage late genes by two mechanisms: derepression of P2 prophage and transactivation of P2 late-gene promoters. P4 also exploits the morphopoietic pathway of P2 by controlling the capsid size to fit its smaller genome. The P4 sid gene product is responsible for capsid size determination, and the P2 capsid gene product, gpN, is used to build both sizes. The P2 capsid contains 420 capsid protein subunits, and P4 contains 240 subunits. The size reduction appears to involve a major change of the whole hexamer complex. The P4 particles are less stable to heat inactivation, unless their capsids are coated with a P4-encoded decoration protein (the psu gene product). P4 uses a small RNA molecule as its immunity factor. Expression of P4 replication functions is prevented by premature transcription termination effected by this small RNA molecule, which contains a sequence that is complementary to a sequence in the transcript that it terminates.

Mutations in the alpha subunit of RNA polymerase that affect the regulation of porin gene transcription in Escherichia coli K-12

The two-component regulatory system consisting of OmpR and EnvZ controls the differential expression of major outer membrane porin proteins OmpF and OmpC of Escherichia coli K-12. We have isolated and characterized two mutations in rpoA, the gene encoding the alpha subunit of RNA polymerase, that decrease the expression of OmpF. These mutations have a number of properties that distinguish them from previously isolated rpoA mutations that affect porin expression. The rpoA203 mutation decreases the expression of porin genes ompF and ompC and also decreases the expression of the malE and phoA genes. In contrast, rpoA207 decreases the expression of ompF but does not affect ompC, malE, or phoA transcription. Our results suggest that mutations at various positions in the alpha subunit may affect the OmpR-dependent transcription of ompF and ompC differently and may be useful for analyzing the mechanism underlying their differential expression in response to medium osmolarity.

Nucleotide sequence of the adi gene, which encodes the biodegradative acid-induced arginine decarboxylase of Escherichia coli

Arginine decarboxylase (encoded by adi) is induced under conditions of acidic pH, anaerobiosis, and rich medium. The DNA sequence of a 3-kb fragment of the Escherichia coli chromosome encoding biodegradative arginine decarboxylase was determined. This sequence encodes a protein of 755 amino acids with a molecular size of 84,420 daltons. The molecular weight and predicted Adi amino acid composition agree with those found in earlier work. The amino acid sequence of arginine decarboxylase showed homology to those of three other decarboxylases of E. coli: (i) CadA, encoding lysine decarboxylase; (ii) SpeC, encoding biosynthetic ornithine decarboxylase; and (iii) SpeF, encoding biodegradative ornithine decarboxylase and the lysine decarboxylase of Hafnia alvei. Unlike SpeC and SpeF, Adi is not similar to the biosynthetic arginine decarboxylase, SpeA. adi is also dissimilar to cadA and speF in that it does not appear to be part of an operon containing a metabolically related transport protein, indicating that it represents a new type of biodegradative decarboxylase regulation. Transcriptional fusions between fragments upstream of adi and lacZ, primer extension, and site-directed mutagenesis experiments defined the pH-regulated promoter. Deletion analysis of the upstream region and cloning of fragments to make adi::lacZ protein fusion implicated a region beyond an upstream SspI site in pH regulation. Induction of adi in the presence of sublethal concentrations of novobiocin or coumermycin A1, inhibitors of DNA gyrase, was dramatically decreased, indicating that DNA supercoiling is involved in adi expression. These results and those of promoter structure studies indicated that acid regulation of adi may involve a mechanism different from that of acid regulation of cad.

Involvement of the Escherichia coli RNA polymerase alpha subunit in transcriptional activation by the bacteriophage lambda CI and CII proteins

Escherichia coli cells harbouring the rpoA341 mutation produce an RNA polymerase which transcribes inefficiently certain operons subject to positive control. Here, we demonstrate that the rpoA341 allele also prevents lysogenization of the host strain by bacteriophage lambda, a process dependent upon the action of two phage-encoded activators. This phenomenon was shown to arise from an inability to establish an integrated prophage rather than a failure to maintain the lysogenic state. The inability of the rpoA341 host to support lysogenization could be completely reversed by CII-independent expression of int and cI in trans. These results led us to propose that the inhibition of lysogenization arises from a defective interaction between the phage lambda transcriptional activator CII and the mutant RNA polymerase at the phage promoters pI and pE. Finally, we also provide genetic evidence for impaired transcription of the cI gene from the CI-activated promoter, pM in the rpoA341 background.

Site-directed mutagenesis of an amino acid residue in the bacteriophage P2 ogr protein implicated in interaction with Escherichia coli RNA polymerase

The P2 ogr gene encodes a 72-amino-acid protein required for P2 late gene expression. This gene was defined originally by a class of compensatory mutations which overcome the block to P2 late transcription imposed by a host mutation, rpoA109, in the gene encoding the alpha subunit of Escherichia coli RNA polymerase. Spontaneous compensatory ogr mutations substitute a Cys for a Tyr residue at amino acid 42 in the Ogr polypeptide. Using suppression of an ogr amber mutation and site-directed oligonucleotide mutagenesis, we have studied the effect of amino acid substitutions at this position in Ogr. Substitution of charged residues at this site renders Ogr protein inactive, in rpoA+ and rpoA109 strains. While 11 different amino acids are capable of replacing the wild-type Tyr-42 to allow P2 growth to varying degrees in a wild-type E. coli strain, only three of these allow phage growth in strains carrying the rpoA109 mutation. Phages carrying Cys or Ala in place of Tyr-42 gave burst sizes at least as high as P2 ogr+ in a rpoA+ strain; a Gly substitution also allowed P2 to grow in either a rpoA+ or rpoA109 background, but markedly reduced the burst size. These results are consistent with a direct interaction between Ogr and the alpha subunit of E. coli RNA polymerase in positive control of P2 late transcription, and indicate that the block imposed by the rpoA109 mutation is due to steric hindrance.

Escherichia coli K-12 and B contain functional bacteriophage P2 ogr genes

The bacteriophage P2 ogr gene encodes an essential 72-amino-acid protein which acts as a positive regulator of P2 late transcription. A P2 ogr deletion phage, which depends on the supply of Ogr protein in trans for lytic growth on Escherichia coli C, has previously been constructed. E. coli B and K-12 were found to support the growth of the ogr-defective P2 phage because of the presence of functional ogr genes located in cryptic P2-like prophages in these strains. The cryptic ogr genes were cloned and sequenced. Compared with the P2 wild-type ogr gene, the ogr genes in the B and K-12 strains are conserved, containing mostly silent base substitutions. One of the base substitutions in the K-12 ogr gene results in replacement of an alanine with valine at position 57 in the Ogr protein but does not seem to affect the function of Ogr as a transcriptional activator. The cryptic ogr genes are constitutively transcribed, apparently at a higher level than the wild-type ogr gene in a P2 lysogen.

Suppressor mutations in rpoA suggest that OmpR controls transcription by direct interaction with the alpha subunit of RNA polymerase

We have isolated mutations in rpoA, the gene encoding the alpha subunit of RNA polymerase, that specifically affect transcriptional control by OmpR and EnvZ, the two-component regulatory system that controls porin gene expression in Escherichia coli. Characterization of these mutations and a previously isolated rpoA allele suggests that both positive and negative regulation of porin gene transcription involves a direct interaction between OmpR and RNA polymerase through the alpha subunit. Several of the rpoA mutations cluster in the carboxy-terminal portion of the alpha protein, further suggesting that it is this domain of alpha that is involved in interaction with OmpR and perhaps other transcriptional regulators as well.

Mutations in rpoA affect expression of anaerobically regulated genes in Salmonella typhimurium

oxrB8, a mutation that diminishes the anaerobic induction of pepT and other anaerobically regulated, oxrA (fnr)-dependent Salmonella typhimurium genes, is an allele of rpoA, the gene for the alpha subunit of RNA polymerase. Four additional rpoA mutations that affect anaerobic pepT expression have been isolated after localized mutagenesis of the rpoA region. All but one of these rpoA mutations appear to have relatively specific effects on genes that require the OxrA (FNR) protein, a positive transcriptional regulator of a family of anaerobically expressed genes. All of these mutations lead to amino acid substitutions in the C-terminal region of the alpha subunit. These results taken with a number of previous observations suggest a role for the alpha subunit in the interaction between RNA polymerase and positive transcriptional regulatory proteins. They also suggest that the C-terminal region of alpha is important for these interactions.

Escherichia coli rpoA mutation which impairs transcription of positively regulated systems

The rpoA341 (phs) mutation of Escherichia coli results in decreased expression of several positively regulated operons and has been mapped to within or very near the rpoA gene encoding the alpha subunit of RNA polymerase. We have shown that plasmid-directed synthesis of the wild-type alpha subunit can complement the defective phenotypes associated with this mutation consistent with its proposed location within rpoA. This mutation was mapped by marker rescue to within a 182bp region near the 3' end of rpoA and was subsequently transferred to a plasmid by recombination in vivo. DNA sequence analysis revealed that the RpoA341 phenotype was the result of the substitution of lysine 271 by glutamate within the alpha polypeptide. We discuss this result in relation to our current understanding of the functional organization of the alpha subunit.

Bipartite functional map of the E. coli RNA polymerase alpha subunit: involvement of the C-terminal region in transcription activation by cAMP-CRP

The alpha subunit of Escherichia coli RNA polymerase plays a major role in the subunit assembly. Carboxyterminal deletion derivatives lacking 73 or 94 amino acid residues were assembled in vitro into enzyme molecules. Core enzymes consisting of these C-terminal-truncated alpha subunits were as active in RNA synthesis as native core enzyme. By the addition of sigma 70 subunit, these mutant enzymes initiated transcription from certain promoters. The mutant RNA polymerases, however, did not show cAMP-CRP activated transcription. These results demonstrate that the N-terminal region of the alpha subunit is involved in the formation of active enzyme molecule, while the C-terminal region plays an essential role in response to transcription activation by cAMP-CRP.

Deletion analysis of a bacteriophage P2 late promoter

We have fused the promoter (PF) for the P2 late FETUD operon to the gene (cat) encoding chloramphenicol acetyltransferase (CAT) in a plasmid vector. Synthesis of CAT in Escherichia coli strains carrying this plasmid requires the product of the P2 ogr gene or the satellite phage P4 transactivation gene, delta. Our results demonstrate that these phage-encoded transcriptional regulatory proteins are necessary and sufficient for activation of P2 late transcription in this reporter plasmid. Positive regulation of cloned PF is severely impaired in a host strain carrying the rpoA109 mutation. Expression from the cloned promoter thus approximates those features of P2 late transcription that have been shown to occur during normal P2 infection. To define sequences required for promoter function, sequential upstream deletions of PF were generated using BAL 31 nuclease, and the mutant promoters were assayed for cat expression. A sequence between nucleotides -69 and -64 from the transcription start point was found to be essential for promoter activity. This coincides with a region of homology conserved among all four P2 late gene promoters and the two P4 late promoters, and includes an element of dyad symmetry.

Sequence analysis of two temperature-sensitive mutations in the alpha subunit gene (rpoA) of Escherichia coli RNA polymerase

The rpoA gene of Escherichia coli encodes the alpha subunit of the DNA-dependent RNA polymerase. Two mutant alleles, rpoA101 and rpoA112, both of which produce RNA polymerase with altered thermostability and reduced fidelity of transcription in vitro (Ishihama et al. (1980) J. Mol. Biol. 137, 137-150), have been analyzed in details. The mutations were found to be responsible for the temperature-sensitive growth by complementation test using a rpoA-expression plasmid. Each mutant allele was amplified from total cell DNA by PCR (polymerase chain reaction) and directly sequenced. Both the mutant rpoA genes were found to carry a single base transition which leads to a substitution of Cys for Arg at the position 191 (rpoA101) or 45 (rpoA112), respectively. Since the rpoA112 mutation causes the defect in RNA polymerase assembly (Kawakami & Ishihama (1980) Biochemistry 19, 3491-3495), the amino-terminal region of alpha including the position 45 was considered to play an important role in subunit assembly.

A mutation of the transactivation gene of satellite bacteriophage P4 that suppresses the rpoA109 mutation of Escherichia coli

Satellite bacteriophage P4 requires the products of the late genes of a helper such as P2 in order to grow lytically. The Escherichia coli rpoA109 mutation, which alters the alpha subunit of RNA polymerase, prevents transcription of the late genes of bacteriophage P2. Suppressor mutations that define the P2 ogr gene overcome this block. We found that P4 lytic growth using a P2 ogr+ prophage helper was prevented by the rpoA109 mutation but that this block was overcome when the P2 helper carried the suppressor mutation in the ogr gene. Furthermore, we isolated and characterized four independent mutations in P4, called org, that suppress the E. coli rpoA109 mutation by allowing P4 lytic growth using a P2 ogr+ helper. DNA sequence analysis revealed that the four independent org mutations are identical and that they occur in the P4 delta gene, which codes for a factor that positively regulates the transcription of the P2 and P4 late genes. delta is predicted to code for a basic 166-amino-acid residue protein. Each 83-residue half of the predicted delta gene product is similar to the predicted 72-residue proteins encoded by the ogr gene of P2 and the B gene of phage 186.

A temperature-sensitive mutant of Escherichia coli affected in the alpha subunit of RNA polymerase

A temperature-sensitive mutant of Escherichia coli affected in the alpha subunit of RNA polymerase has been investigated. Gene mapping and complementation experiments placed the mutation to temperature-sensitivity within the alpha operon at 72 min. on the bacterial chromosome. The rate of RNA synthesis in vivo and the accumulation of ribosomal RNA were significantly reduced in the mutant at 44 degrees C. The thermostability at 44 degrees C of the purified holoenzyme from mutant cells was about 20% of that of the normal enzyme. Assays with T7 DNA as a template showed that the fraction of active enzyme competent for transcription was reduced as a function of assay temperature but that initiation and elongation were not significantly affected by the alpha mutation. A major effect on the fidelity of transcription was observed with the mutant enzyme, with misincorporation on two different templates stimulated about 4 fold at 37 degrees C. The role of the alpha dimer in the structure and function of RNA polymerase is discussed.

Directed mutagenesis of the bacteriophage P2 ogr gene defines an essential function

The ogr gene of bacteriophage P2 codes for a basic protein of 72 amino acids which is thought to be essential for activation of P2 late gene transcription. However, conditionally lethal mutations in the ogr gene have never been isolated. We have constructed a P2 ogr deletion mutant by in vitro techniques. This deletion phage, P2-del15, grows in a host which provides the ogr gene product in trans from a plasmid but fails to grow in hosts lacking the ogr plasmid. This demonstrates that the ogr gene is essential for P2 lytic growth. The deletion in P2del15 has removed about half of the carboxy-terminal part of the ogr gene. The transcript from this deletion mutant can be distinguished from the wild-type transcript by S1 nuclease protection. The analysis of such transcripts suggests that the ogr gene product may negatively regulate its own transcription.

The rpoA341 allele of Escherichia coli specifically impairs the transcription of a group of positively-regulated operons

The specificity of the transcription defect caused by the rpoA341(phs) allele has been investigated. Three apparently unlinked genetic systems have been found to be impaired in their transcription by this mutant allele of the alpha subunit of RNA polymerase. These three systems, the melAB operon, the cysA locus and the ara regulon, are apparently unrelated other than by their requirement for a regulon-specific positive regulator for the initiation of transcription. Expression of the gene for the positive regulator does not appear to be significantly affected in any of the three systems. However, mutations that render expression of the araBAD operon independent of the regulatory protein also confer insensitivity to the rpoA341 allele. The significance of these observations is discussed in the context of models of positive regulation.

A deficiency in cyclic AMP results in pH-sensitive growth of Escherichia coli K-12

Mutants of Escherichia coli K-12 deficient in adenyl cyclase (cya) and catabolite activator protein (crp) have been shown to grow more slowly than their parent strains in glucose-minimal medium. Their growth rate decreased markedly with increasing pH between 6 and 7.8. We have shown that this pH sensitivity is a direct consequence of the cya mutation, because a mutation to pH resistance also restored ability to ferment a variety of sugars. The proton motive force-dependent uptake of proline and glutamate was also reduced and sensitive to pH in the cya mutant. The membrane-bound ATPase activity was normal. The rate of oxygen uptake by cells, although reduced, was pH insensitive. We suggest several explanations for this phenotype, including a possible defect in energy transduction.

Physical mapping of the K+ transport trkA gene of Escherichia coli and overproduction of the TrkA protein

The position on the Escherichia coli chromosome of trkA, a gene coding for a membrane protein involved in K+ transport by the constitutive uptake system Trk, was determined. We observed that the gene is transcribed in a clockwise direction and that it is located at 72.4 min on the chromosome in a 1.75-kilobase NruI-EcoRV DNA fragment 1.0 kilobase upstream of rplQ. We localized an additional gene encoding a 17,000-molecular-weight protein of unknown function between the trkA and rplQ genes. A plasmid, pDB3, was constructed in which the transcription of the trkA gene was put under the control of the lambda pL promoter. pDB3-containing cells of a strain, which contained the temperature-sensitive lambda repressor cI857 in the chromosome, overproduced the 53,000-molecular-weight TrkA protein at the nonpermissive temperature to such an extent that TrkA became the major cell protein. From cell fractionation studies, we conclude that the overproduced TrkA protein forms aggregates.

Isolation of mutations in the alpha operon of Escherichia coli that suppress the transcriptional defect conferred by a mutation in the porin regulatory gene envZ

One class of mutations in the envZ gene of Escherichia coli K-12 confers a pleiotropic defect on the expression of several genes, including ompF, lamB, and phoA, that are otherwise not commonly regulated. Four second-site mutations that suppress this transcriptional defect have been isolated by using a procedure that circumvented the problem of intragenic suppressors, including true revertants. All four mutations have been mapped to the genes of the alpha operon and have been assigned tentatively to the gene rpoA, which specifies the alpha subunit of RNA polymerase. The mutations, referred to as sez (for suppressor of envZ), did not appear to confer a phenotype on an otherwise wild-type strain and did not suppress the transcriptional defects conferred by several other phenotypic classes of envZ mutations, including amber mutations. Our results led us to postulate that the alpha subunit or some other component of the alpha operon plays a role in determining the specificity of gene expression.

Osmotic regulation of transcription: induction of the proU betaine transport gene is dependent on accumulation of intracellular potassium

The proU locus, which encodes a high-affinity betaine transport system, and the kdp operon, which encodes a potassium transport system, are the principal osmoresponsive genes in Escherichia coli and Salmonella typhimurium. The kdp operon is known to be induced in response to changes in cell turgor. We have investigated the control of proU expression and shown that it differs from that of kdp in a number of fundamental ways. Rather than responding to changes in turgor, proU expression is principally determined by the intracellular accumulation of potassium ions. Potassium and betaine were shown to play distinct osmoprotective roles. Potassium serves as the principal osmoprotectant and is accumulated in response to low-level osmotic stress to restore turgor. As external osmolarity is increased to a level at which the corresponding increase in internal potassium concentrations is potentially deleterious to enzyme function, betaine (when available) is accumulated in preference to potassium. The different mechanisms of proU and kdp regulation reflect the different physiological roles of these two osmoprotectants.

Gene for the alpha subunit of Bacillus subtilis RNA polymerase maps in the ribosomal protein gene cluster

We isolated the gene encoding the alpha subunit of Bacillus subtilis RNA polymerase from a lambda gt11 expression vector library by using anti-alpha antibody as a probe. Four unique clones were isolated, one carrying a lacZ-alpha gene fusion and three carrying the entire alpha coding region together with additional sequences upstream. The identity of the cloned alpha gene was confirmed by the size and immunological reactivity of its product expressed in Escherichia coli. Further, a partial DNA sequence found the predicted NH2 terminus of alpha homologous with E. coli alpha. By plasmid integration and PBS1 transduction, we mapped alpha near rpsE and within the major ribosomal protein gene cluster on the B. subtilis chromosome. Additional DNA sequencing identified rpsM (encoding S13) and rpsK (encoding S11) upstream of alpha, followed by a 180-base-pair intercistronic region that may contain two alpha promoters. Although the organization of the alpha region resembles that of the alpha operon of E. coli, the putative promoters and absence of rpsD (encoding S4) immediately preceding the B. subtilis alpha gene suggest a different regulation.

Phenotypic properties of a unique rpoA mutation (phs) of Escherichia coli

The phs mutation of Escherichia coli has been suggested to affect the Na+/H+ antiport (D. Zilberstein, E. Padan, and S. Schuldiner, FEBS Lett. 168:327-330, 1980). We have recently shown that the mutation affects the rpoA gene and thus affects transcription. The extent of the pleiotropy of the phs mutation was investigated. In addition to the previously reported growth defect on L-glutamate and melibiose, the mutation also affects at least two other metabolic systems. The transport and metabolism of arabinose is impaired and the transport of sulfate is reduced. The extent to which the effects of the phs mutation on metabolism are due to a defect in the Na+/H+ antiport was investigated, and no causal role for this transport system in the metabolic defects was found.