Histidine Regulation in Salmonella typhimurium
IX. HISTIDINE TRANSFER RIBONUCLEIC ACID OF THE REGULATORY MUTANTS
Michael Brenner 1 and Bruce N. Ames 1
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1 From the Biochemistry Department, University of California, Berkeley, California 94720
Four classes of mutants constitutive for the histidine operon of Salmonella typhimurium, hisR, hisT, hisU, and hisW, were examined for a possible role in the production of histidine tRNA. The content of tRNAhis in tRNA isolated from each of the mutant types was compared to that of the wild type, and the chromatographic behavior of the tRNAhis obtained from the mutants and the wild type was examined. Chromatography of the tRNAhis of the wild type gave no evidence for multiple species.
Two factors suggest that hisR is a structural gene for histidine tRNA. First, hisR strains were found to have 25 to 45% less tRNAhis than the wild type; and second, introduction of an episome carrying the hisR gene into the wild type resulted in a 2.5-fold increase in the quantity of tRNAhis.
The tRNAhis of a hisT mutant chromatographed differently from that of the wild type. Since the hisT gene has previously been shown to code for a dispensible protein, we conclude that this protein is involved in tRNAhis maturation. The tRNAhis from hisT mutants is present in normal amounts, is charged normally, and appears to behave normally in protein synthesis, although not in repression control.
The tRNA from a cold-sensitive hisW mutant was found to have an altered acceptance for several amino acids. This indicates that hisW also codes for a tRNA maturation enzyme. No increase in tRNAhis levels was obtained when an episome carrying the hisW gene was inserted into the wild type, and the tRNAhis from a hisW mutant behaved as the tRNA from the wild type on chromatography.
No difference was found between the tRNAhis of hisU mutants and that of the wild type.
Submitted on September 23, 1971
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