Characterization of mutants with single and multiple defects in the tryptophan biosynthetic pathway in Bacillus subtilis

Novel form of transcription attenuation regulates expression the Bacillus subtilis tryptophan operon

Transcription of the trp operon of Bacillus subtilis is regulated in response to the availability of tryptophan. The first structural gene of the operon is preceded by a 204-base-pair transcribed leader region that contains a segment with the features of a procaryotic termination site. Transcription of the leader region was analyzed in vivo and in vitro to determine whether this putative termination site was used to regulate operon expression. When RNA was isolated from wild-type cells grown in the presence of excess tryptophan, transcripts of the operon ended at the putative termination site. In contrast, RNA isolated from cells grown in the absence of tryptophan or from a mutant strain which is constitutive for trp operon expression contained trp transcripts that extended beyond the termination site into the structural genes. To assess termination quantitatively in vivo, a trpE-lacZ fusion was constructed in which the trp promoter and leader region controls hybrid beta-galactosidase formation. The effects on hybrid beta-galactosidase levels of point mutations and deletions introduced into this leader region were determined. The results obtained establish that transcription of the trp operon structural genes is regulated in the leader region. This regulation appears to be mediated by the formation of alternative secondary structures of the leader transcript. In vitro transcription studies with wild-type and mutant templates provided additional evidence that the identified alternative RNA secondary structures regulate transcription termination. We hypothesize that binding of a tryptophan-activated regulatory protein to a specific segment of the nascent leader transcript prevents formation of one of the alternative secondary structures, thereby directing RNA polymerase to terminate transcription.

Construction of a promoter-probe vector for a Bacillus subtilis host by using the trpD+ gene of Bacillus amyloliquefaciens

The trp gene cluster of Bacillus amyloliquefaciens was found to be structurally similar to that of the Enterobacteriaceae. The translation termination codon of the putative trpE gene and the initiation codon for the putative trpD gene overlap at the trpE-trpD junction, and a promoter for the putative trpC gene is suggested to exist. A promoter-probe vector of Bacillus subtilis, pFTB281, was constructed with a DNA fragment of B. amyloliquefaciens, complementing the trpC and trpD mutations of B. subtilis, a 42-base-pair DNA fragment of M13mp7, and the larger EcoRI-PvuII fragment of pUB110, which confers an autonomous replication function and the kanamycin-resistance phenotype to the chimeric plasmid. pFTB281 has BamHI, EcoRI, and SalI cloning sites in the 5'-upstream portion of the protein-coding region of the putative trpD gene, and the insertion of a certain DNA fragment at any of these sites allowed the plasmid to transform a trpD mutant of B. subtilis to the TrpD+ phenotype. DNA fragments showing the promoter function for the trpD gene were obtained from B. amyloliquefaciens and Saccharomyces cerevisiae chromosomes and rho 11 and lambda phage DNAs, but rarely from the DNAs of Escherichia coli and pBR322.

Isolation and characterization of two tryptophan biosynthetic enzymes, indoleglycerol phosphate synthase and phosphoribosyl anthranilate isomerase, from Bacillus subtilis

Two of the enzymes responsible for tryptophan biosynthesis in Bacillus subtilis have been extensively purified. These proteins are indole-3-glycerol phosphate synthase and N-(5'-phosphoribosyl) anthranilate isomerase. By comparison to the non-differentiating enteric bacteria in which these two enzymes are fused into a single polypeptide, the isolation of the indoleglycerol phosphate synthase and phosphoribosyl anthranilate isomerase from B. subtilis has demonstrated that the two proteins are separate species in this organism. The two enzymes were clearly separable by anion-exchange chromatography without any significant loss of activity. Molecular weights were determined for both enzymes by gel filtration and sodium dodecyl sulfate-slab gel electrophoresis, and indicated that the indoleglycerol phosphate synthase is the slightly larger of the two proteins. The minimum molecular weight for indoleglycerol phosphate synthase was 23,500, and that for phosphoribosyl anthranilate isomerase was 21,800. Both enzymes have been examined as to conditions necessary to achieve maximal activity of their individual functions and to maintain that activity.

Genetics and biochemistry of pyrimidine biosynthesis in Bacillus subtilis: linkage between mutations resulting in a requirement for uracil

A number of independently derived uracil-requiring mutant strains of the parent strain 168 were mapped by inter-mutant transformation crosses. Only a few of these mutant strains were found to be transformable. Studies were performed in which these transformable uracil-requiring mutant strains were used as the recipient of deoxyribonucleic acid extracted from phenotypically similar mutant strains. The results yielded data resulting in a fine-structure map in which all mutations were found to be linked in a small region corresponding to that previously published as the uracil region of the Bacillus subtilis genome.

Tryptophan biosynthetic enzymes of Staphylococcus aureus

Tryptophan biosynthetic enzymes were assayed in various tryptophan mutants of Staphylococcus aureus strain 655 and the wild-type parent. All mutants, except trpB mutants, lacked only the activity corresponding to the particular biosynthetic block, as suggested previously by analysis of accumulated intermediates and auxonography. Tryptophan synthetase A was not detected in extracts of either trpA or trpB mutants but appeared normal in other mutants. Mutants in certain other classes exhibited partial loss of another particular tryptophan enzyme activity. Tryptophan synthetase B activity was not detected in cell extract preparations but was detected in whole cells. The original map order proposed for the S. aureus tryptophan gene cluster was clarified by the definition of trpD (phosphoribosyl transferase(-)) and trpF (phosphoribosyl anthranilate isomerase(-)) mutants. These mutants were previously unresolved and designated as trp(DF) mutants (anthranilate accumulators). Phosphoribosyl anthranilate isomerase and indole-3-glycerol phosphate synthetase enzymes were separable by molecular sieve chromatography, suggesting that these functions are coded by separate loci. Molecular sieve chromatography failed to reveal aggregates involving anthranilate synthetase, phosphoribosyl transferase, phosphoribosyl anthranilate isomerase, and indole-3-glycerol phosphate synthetase, and this procedure provided an estimate of the molecular weights of these enzymes. Tryptophan was shown to repress synthesis of all six tryptophan biosynthetic enzymes, and derepression of all six activities was incident upon tryptophan starvation. Tryptophan inhibited the activity of anthranilate synthetase, the first enzyme of the pathway.

Anthranilate synthase-anthranilate 5-phosphoribosyl 1-pyrophosphate phosphoribosyltransferase from Aerobacter aerogenes

1. Anthranilate synthase and phosphoribosyltransferase from Aerobacter aerogenes purify simultaneously and sediment together on sucrose gradients, showing that they occur as an enzyme aggregate. Both activities of the intact aggregate are subject to inhibition by tryptophan. 2. By using appropriate auxotrophic mutants it was shown that an intact active enzyme aggregate is formed when the components come from separate mutant strains. An intact active aggregate can also be formed when one component is from Escherichia coli and the other from A. aerogenes. 3. Phosphoribosyltransferase of A. aerogenes is active when not in an aggregate with anthranilate synthase, but is not subject to tryptophan inhibition, indicating that the inhibitor site is on the anthranilate synthase component. 4. Anthranilate synthase can be active and sensitive to tryptophan inhibition when complexed with an inactive phosphoribosyltransferase. 5. Kinetic studies on the anthranilate synthase activity show that tryptophan is a competitive inhibitor with respect to chorismate and a non-competitive inhibitor with respect to either glutamine or NH(4) (+) ions. This is consistent with a sequential mechanism of the ordered type in which chorismate is the first reactant.

Inducible uptake system for -carboxy-cis, cis-muconate in a permeability mutant of Pseudomonas putida

A procedure for the large-scale enzymatic synthesis of beta-carboxymuconate is described. When used as a growth substrate, beta-carboxymuconate selected for mutant strains of Pseudomonas putida that were permeable to polycarboxylic acid intermediates of the beta-ketoadipate pathway. One mutant organism, strain PRS2110, was investigated in detail. It differed from the parental strain in that it possessed a beta-carboxymuconate uptake system that was formed when the compound was supplied exogenously to the cells. The uptake system was not induced by beta-carboxymuconate supplied endogenously during growth with p-hydroxybenzoate. These observations suggested that beta-carboxymuconate was contained within a physical compartment of enzymes during growth with p-hydroxybenzoate. Support for this hypothesis came from the demonstration that enzymes of the beta-ketoadipate pathway were held together by weak chemical interactions during the chromatography of crude extracts of benzoategrown P. putida on diethylaminoethyl-cellulose columns.

Enzymes of tryptophan biosynthesis in Serratia marcescens

In Serratia marcescens, the tryptophan biosynthetic enzymes were formed coordinately. A number of tryptophan auxotrophs showed single biochemical lesions; several mutants showed pleiotropic effects. Sucrose density gradient centrifugation revealed an unique pattern of migration of the tryptophan biosynthetic enzymes. The repression response of the Serratia enzymes to exogenous tryptophan was fivefold more sensitive than that found in Escherichia coli. When this information is contrasted with the available information on the other Enterobacteriaceae, one is compelled to conclude that S. marcescens enjoys a rather marked evolutionary divergence from the other enteric organisms.

Antimetabolite action of 5-methyltryptophan in Bacillus subtilis

The roles of anthranilate and histidine in the regulation of tryptophan synthesis were implicated by observations of antagonistic relationships with 5-methyltryptophan in Bacillus subtilis.