The psu1+ amber suppressor gene of bacteriophage T4: identification of its amino acid and transfer RNA

Previous work identified the psu⁺₁ amber suppressor gene of bacteriophage T4. Analysis of protein arising from suppression now shows that psu⁺₁ specifies the insertion of serine in response to the amber triplet. The efficiency of suppression is 70%.The psu₁⁺ gene affects a serine transfer RNA coded by bacteriophage T4. Comparative ribonuclease T₁ fingerprint analysis of the serine transfer RNAs made by wild type T4 and psu⁺₁ strains shows a specific alteration in the patterns, presumably reflecting a mutational alteration in the anticodon of the transfer RNA. Mutations which result in the loss of suppressor activity define two genes: one is apparently the structural gene for the serine transfer RNA; the function of the second gene, M1, is less clear. Mutational inactivation of either gene prevents the appearance of the serine transfer RNA and a second transfer RNA, which has not yet been associated with its cognate amino acid. M1 mutants are also deficient in the production of several additional transfer RNA species, as well as several larger RNAs. The significance of these results in relation to transfer RNA biosynthesis is discussed.