The Nucleotide Sequences of Tyrosine Transfer RNAs of Escherichia coli

The tyrosine tRNAs specified by the E. coli amber suppressor gene su:,, and the wild type non-suppressing allele su,, were selectively labelled with 32P in E. coli infected with transducing phage p80 carrying either of these genes. The determination of the nucleotide sequence of the SU:,, tyrosine tRNA is described. This tRNA has the anticodon CUA. The su~, tRNA differs from su:,, tRNA by a single nucleotide and has the anticodon GUA where G is a modified guanylic acid residue. E. coli su- cells contain two tyrosine tRNAs (I and 11). The determination of the nucleotide sequence of these is described. Species I is identical to su,, tRNA while species I1 differs by two nucleotides in the variable loop region. * * E. coli normally contains two types of tyrosine tRNA (I and 11) differing from each other by two nucleotides in the region between the anticodon stem and the stem of the ‘TYCG loop’. There are two identical structural genes for tyrosine tRNA I, while the gene(s) for tyrosine tRNA I1 has not been located. The amber suppressor SUIII gene is one of the two structural genes for tyrosine tRNA I. In suppressor strains SU:,, this gene has mutated to give a species of tyrosine tRNA I which can recognise the codon UAG. This su:,, tRNA differs from tyrosine tRNA I by a change in the first base of its anticodon. These results have been briefly reported by Goodman et al. [l] and this communication describes the detailed determination of the three different tyrosine tRNA sequences in E. coli: namely su:,,; sunI and tRNA I (which are identical); and tRNA 11. In the sequence determinations we used the methods developed by Sanger et al. [2] and Brownlee and Sanger [3] applicable to small amounts of high specific activity 32P-labelled tRNA. Quite apart from the rapidity and simplicity of these methods, their use was dictated by the technique for preparing the su:,, and su;, tRNAs, which were isolated after infection of bacteria by transducing phages carrying the SUIII gene as either the + or - allele. The infected cells contain