Strains overproducing tRNA for histidine.

Hybridization analysis of total genomic DNA indicated that Escherichia coli K12 contains a single copy of the gene encoding the histidine-accepting tRNA. This gene was subcloned onto an inducible expression vector under the control of the tac promoter. Strains carrying the resulting plasmid showed five- to six-fold increased histidine-accepting activity after induction. This overproduction of tRNAHis did not effect the growth rate of the strain or lead to derepression of the histidine biosynthetic enzymes. Neither did it have an effect on mistranslation elicited by histidine starvation. However, in cells starved for histidine by the addition of alpha-methyl histidine, the overproduction of tRNAHis interfered with the ability of the cells to recover from starvation.