A mutant of Escherichia coli defective in leucyl, phenylalanyl-tRNA-protein transferase.

A mutant of E. coli that lacks leucyl,-phenylalanyl-tRNA-protein transferase (EC 2.3.2.6) has been isolated. Ability to produce the two activities could be introduced into the mutant from an F' strain whose episome contains genetic material located between 45 and 54 min on the E. coli chromosome. When grown into stationary phase and resuspended in minimal medium with glycerol, the mutant exhibited a marked lag before resuming growth. Revertants that did not show this lag were selected and were found to have regained both transfer activities. Extracts of wild-type, mutant, and revertant strains were compared as acceptors for the enzymatic transfer of radioactive phenylalanine. Analysis of the labeled polypeptides by disc gel electrophoresis indicated that certain potential acceptors may be preferentially acylated in vivo. These data provide genetic confirmation that the same enzyme protein catalyzes the transfer of leucine and phenylalanine and suggest that leucyl,phenylalanyl-tRNA-protein transferase is involved in a growth regulatory mechanism.