Transfer Ribonucleic Acid Nucleotidyl-transferase Plays an Essential Role in the Normal Growth of Escherichia coli and in the Biosynthesis of Some Bacteriophage T4 Transfer Ribonucleic Acids

Abstract

A series of cca mutants, deficient in the enzyme tRNA nucleotidyltransferase, have been used to show that this activity is essential for the normal growth of Escherichia coli and for the biosynthesis of some tRNAs. In some genetic backgrounds cca mutants grew at slow rates, and their generation time was related to the amount of residual tRNA nucleotidyltransferase remaining in the cells. Mutants with greater than 15 % of activity grew normally, indicating that the enzyme was usually present in large excess. One cca mutant, containing less than 5 % of normal activity, was used to select fast growing revertants. All revertants to normal growth simultaneously regained tRNA nucleotidyltransferase activity. Genetic studies indicated that the reversion occurred at the cca locus at a rate of 10-8 to 10-9. The importance of tRNA nucleotidyltransferase for tRNA biosynthesis was demonstrated in studies measuring the expression of bacteriophage T4 psu1+ and psu2+ tRNAs in the various cca mutants. Bacteriophage T4 psu1+- and psu2+-amber double mutants plated with very low efficiencies on cca mutants with low enzyme activity, and the plating efficiency increased with increasing levels of enzyme in the mutant cells.