Non-coordinate regulation in 5-methyl tryptophan-resistant mutants of Bacillus subtilis

Cotransductional mapping of the trp-his region of Bacillus megaterium

Eight trp mutations (four trpE, two trpB, one trpC, and one trpD) have been mapped in Bacillus megaterium QM B1551 and were found to be linked to two hisH mutations and unlinked to several other his mutations.

Temperature-induced derepression of tryptophan biosynthesis in a tryptophanyl-transfer ribonucleic acid synthetase mutant of Bacillus subtilis

A tryptophanyl-transfer ribonucleic acid (tRNA) synthetase (l-tryptophan: tRNA ligase adenosine monophosphate, EC 6.1.1.2) mutant (trpS1) of Bacillus subtilis is derepressed for enzymes of the tryptophan biosynthetic pathway at temperatures which reduce the growth rate but still allow exponential growth. Derepression of anthranilate synthase in a tryptophan-supplemented medium (50 mug/ml) is maximal at 36 C, and the differential rate of synthesis is 600- to 2,000-fold greater than that of the wild-type strain or trpS1 revertants. A study of the derepression pattern in the mutant and its revertants indicates that the 5-fluorotryptophan recognition site of the tryptophanyl-tRNA synthetase is an integral part of the repression mechanism. Evidence for a second locus, unlinked to the trpS1 locus, which functions in the repression of tryptophan biosynthetic enzymes is presented.

Regulation of tryptophan biosynthesis in Saccharomyces cerevisiae: mode of action of 5-methyl-tryptophan and 5-methyl-tryptophan-sensitive mutants

In a wild-type strain of Saccharomyces cerevisiae the tryptophan analogue dl-5-methyl-tryptophan (5MT) causes only a slight reduction of the growth rate. Uptake experiments indicate that the limited inhibition is partly due to low levels of 5MT inside the cell. On the other hand, this low concentration of 5MT leads to an increase in the activity of the tryptophan-biosynthetic enzymes. Evidence is presented that suggests that 5MT acts primarily through feedback inhibition of anthranilate synthase, the first enzyme of the pathway. A number of 5MT-sensitive mutants have been isolated, characterized, and assigned to one of the following three classes: class I, strains with altered activity and/or feedback sensitivity of anthranilate synthase; class II, strains with elevated uptake of 5MT; class III, mutants with altered regulation of the tryptophan-biosynthetic enzymes, which do not exhibit increases in activity in the presence of 5MT. This failure to exhibit increased enzyme activities in mutants of class III can also be observed after tryptophan starvation. Two mutants of class III show high sensitivity towards 3-amino-1,2,4-triazole. They can not exhibit derepression of some histidine- and arginine-biosynthetic enzymes under conditions that lead to an increase in these same enzymes in the wild-type strain.

Mapping of the 5-methyltryptophan resistance locus in Bacillus subtilis

The 5-methyltryptophan resistance locus (mtr) in Bacillus subtilis, which leads to constitutive production of the tryptophan enzymes, has been mapped on the chromosome. The order of loci is ser-1-mtr-aroF-aroB-trp-hisB.

Control of tryptophan biosynthesis by the methyltryptophan resistance gene in Bacillus subtilis

5-Methyltryptophan-resistant mutants derived from Bacillus subtilis strain 168 synthesize all of the tryptophan biosynthetic enzymes constitutively and excrete tryptophan. These mutants can be divided into three classes: class 1, low enzyme level and low rate of tryptophan excretion; class 2, high enzyme level and intermediate rate of tryptophan excretion; and class 3, high enzyme level and high rate of tryptophan excretion. A bradytrophic requirement for phenylalanine is correlated with the rate of tryptophan excretion. The phenylalanine requirement is relieved when the rate of tryptophan excretion is reduced by either (i) lowering the level of the tryptophan enzymes, (ii) reducing the supply of a tryptophan precursor (chorismate), or (iii) stopping tryptophan synthesis by a mutational block in the pathway. All of the mutants map in a region of the chromosome previously reported as the mtr locus. Our data show that synthesis of the tryptophan enzymes is controlled through the mtr locus but not influenced by precursors of tryptophan.