GLYCINE CODON DISCRIMINATION AND THE NUCLEOTIDE IN POSITION-32 OF THEANTICODON LOOP

Using an in vitro protein-synthesizing system that allowed us to monit or separately-the reading of each glycine codon, we have previously sh own, that in constructs based on glycine tRNA(1) from Escherichia coli the nature of the nucleotide in position 32 determines the ability of the anticodon UCC to discriminate between the glycine codons. Thus, w ith a U in position 32 the anticodon UCC discriminated according to th e wobble rules, but with a C in this position it had lost its ability to discriminate. In the present paper we show that the same is true al so for constructs based on mycoplasma glycine tRNA. When C32 in the wi ld type was changed to U32, the anticodon UCC discriminated between th e glycine codons, while in wild type mycoplasma glycine tRNA it did no t. Furthermore, when U32 was changed to C32 in glycine tRNA(1) (CCC), the anticodon CCC loses its ability to discriminate. We therefore conc lude that the nature of the nucleotide in position 32 determines the d iscriminatory ability of both anticodons UCC and CCC in the glycine tR NA(1) structural background, and that the same is true for the anticod on UCC in the mycoplasma glycine tRNA background.