Cross pathway regulation of tyrosine and histidine synthesis in Bacillus subtilis. Biochemical, genetic, and transfer RNA studies

Genomewide transcriptional changes associated with genetic alterations and nutritional supplementation affecting tryptophan metabolism in Bacillus subtilis

DNA microarrays comprising approximately 95% of the Bacillus subtilis annotated protein coding ORFs were deployed to generate a series of snapshots of genomewide transcriptional changes that occur when cells are grown under various conditions that are expected to increase or decrease transcription of the trp operon segment of the aromatic supraoperon. Comparisons of global expression patterns were made between cells grown in the presence of indole acrylic acid, a specific inhibitor of tRNA(Trp) charging; cells deficient in expression of the mtrB gene, which encodes the tryptophan-activated negative regulatory protein, TRAP; WT cells grown in the presence or absence of two or three of the aromatic amino acids; and cells harboring a tryptophanyl tRNA synthetase mutation conferring temperature-sensitive tryptophan-dependent growth. Our findings validate expected responses of the tryptophan biosynthetic genes and presumed regulatory interrelationships between genes in the different aromatic amino acid pathways and the histidine biosynthetic pathway. Using a combination of supervised and unsupervised statistical methods we identified approximately 100 genes whose expression profiles were closely correlated with those of the genes in the trp operon. This finding suggests that expression of these genes is influenced directly or indirectly by regulatory events that affect or are a consequence of altered tryptophan metabolism.

[General control of amino acid biosynthesis in Hansenula henricii]

The general control of amino acid biosynthesis was investigated in Hansenula henricii. By limitation for single amino acids in wild type strain and mutants no derepression of enzymes was caused. In prototrophic revertants however, obtained from auxotrophic mutants (his, pdx) enzyme activities were 2 - 17 times higher than in the wild type. In these revertants enzymes of the biosynthetic pathways for tryptophan, phenylalanine, tyrosine, arginine, histidine, cysteine, methionine, asparagine, threonine, and isoleucine were derepressed. The amino acid pool pattern of the revertants if completely different from that in the wild type strain. A discussion of possible mechanisms of general control of amino acid biosynthesis in H. henricii is presented.

Characterization and regulation of anthranilate synthetase from a chloramphenicol-producing streptomycete

In Streptomyces sp. 3022a, anthranilate synthetase is composed of two non-identical subunits. The major subunit (molecular weight, 72,000) converts chorismic acid to anthranilic acid, using ammonia as the source of the amino group. The smaller subunit (molecular weight 28,000 to 29,000) confers on the enzyme the ability to use glutamine instead of ammonia as a substrate. In this study, reactivity with glutamine reached its maximum at pH 7.2 to 7.6, whereas that with ammonia increased linearly through pH 9.0 without reaching a maximum. Activity was increased and stabilized by adding glutamine and magnesium chloride to the buffer system. Both activities of the enzyme were inhibited by anthranilic acid and by tryptophan. Synthesis was repressed by histidine, anthranilic acid, tryptophan, and p-aminobenzoic acid. When activity was repressed by anthranilic acid and by tryptophan, there was a concomitant increase in the activity of arylamine synthetase, an enzyme involved in chloramphenicol production. Stimulating arylamine synthetase, however, did not increase antibiotic synthesis.

Regulation of histidinol phosphate aminotransferase synthesis by tryptophan in Bacillus subtilis

The effect of tryptophan on the synthesis of histidinol phosphate aminotransferase and prephenate dehydrogenase has been examined. The genes specifying two enzymes for tryptophan biosynthesis (anthranilate synthase and tryptophan synthase-B) were found to be derepressed in a temporal sequence according to their chromosomal location. The genes for histidinol phosphate aminotransferase and prephenate dehydrogenase were derepressed simultaneously approximately 8 min after tryptophan synthase-B. When excess tryptophan was added to a derepressed culture, the pattern of repression of trpE (anthranilate synthase), trpB (tryptophan synthase-B), hisH (histidinol phosphate aminotransferase), and tyrA (prephenate dehydrogenase) was found to be simultaneous. Methyl tryptophan-resistant mutants, which synthesize elevated levels of the tryptophan enzymes, also synthesized elevated levels of histidinol phosphate aminotransferase. Qualitatively similar data were obtained in a temperature-sensitive tryptophanyl-transferase ribonucleic acid synthetase mutant grown at elevated temperatures. The time at which messenger ribonucleic acid was synthesized for anthranilate synthase, tryptophan synthase-B, histidinol phosphate aminotransferase, and prephenate dehydrogenase in the presence of actinomycin D indicated that ordered enzyme synthesis was a result of ordered transcription of the corresponding portion of the genome. The effect of the drug rifampin on enzyme synthesis was also examined. The addition of this drug halted the transcription of anthranilate synthase very rapidly, but later regions of the tryptophan region continued to be transcribed. The transcription of the hisH and tyrA genes was also shut off rapidly after rifampin was added. The significance of these observations to the control of transcription of the hisH gene by tryptophan is discussed.

Alteration of tyrosine isoaccepting transfer ribonucleic acid species in wild-type and asporogenous strains of Bacillus subtilis

The relative amounts of two isoacceping species of tyrosine transfer ribonucleic acid, tRNATyrI and tRNATyrII, determined from reversed phase 5 profiles of tyrosyl-tRNA, prepared from Bacillus subtilis strain W168, were growth phase and medium dependent. The growth phase-dependent alterations in the relative amounts of tRNATyr species were also demonstrated in 11 asporogenous strains of B. subtilis. The proportion of tRNA-Tyr species and the extent of the alteration in their relative amounts during the transition from the exponential to the stationary phase of growth of these strains was not directly correlated with the formation of spores by strain W168 grown in various media or the stage at which the asporogenous strains are blocked in the process of sporulation.