Abstract
A number of mutants carrying mutations that occurred near the tryptophan cluster was isolated among 5-methyltryptophan resistant mutants. The mutants showed partially constitutive synthesis of the tryptophan biosynthetic enzymes. Moreover, these mutations affected the expression of the structural genes located in cis-position, but not the genes located in trans-position, suggesting that they represent the operator-constitutive (O °) mutants of the tryptophan operon. Transduction experiments with phage P1 revealed that all the mutations tested are located on the out side of the known polar mutations of the trpE cistron. However, anthranilate synthetase from these mutants is normal in that it is sensitive to allosteric inhibition by tryptophan or 5-methyltryptophan. These results suggest that the mutants are different from the 5-methyltryptophan resistant mutants synthesizing the allosteric-inhibition insensitive enzyme which had been reported by other investigators, and that the operator is distinct from the trpE cistron controlling the structure of anthranilate synthetase. The experiments on disruption of linkage between markers by ultraviolet light irradiation as well as on cotransduction frequencies showed that the length of the region covered by these mutations is about 20 to 30% of that of the total structural genes of the tryptophan operon.
Published Version
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