Evidence for the utilization of host tRNA(m 5 U)methylase to modify tRNA coded by phage T4.

Mutants of Escherichia coli defective only in the biosynthesis of 5-methyluridine (ribothymidine) in their transfer ribonucleic acid (tRNA) were employed to investigate whether phage T4 induces its own tRNA(mV)methylase and whether T4-specific tRNA contains 5-methyluridine. The amounts of other methylated derivatives in the T4-specific tRNA were also determined. The results establish that T4-specific tRNA contains 5-methyluridine, and that there is an absolute requirement for a functional host tRNA(mW)methylase to undertake this modification. Comparison of several physical properties of the host enzyme before and after phage T4 infection did not suggest any phage-directed alteration of the enzyme. The distribution of the methylated constituents in T4-specific tRNA is distinguishable from that in host tRNA. This change, however, may simply reflect a different population of tRNA chains produced by the T4 phage, rather than some change in the tRNA methylase activity of the host: _ -.