volume 9 Number 41981 Nucleic Acids Research UGA suppression by normal tRNATrP in Escherichia coli: codon context effects

The nucleot ide sequences at the 3 ' s ide of in-phase UGA termination codons in mRNAs of various prokaryot ic genes were re-examined. An adenine (A) res idue i s found to be adjacent to the 3 ' s ide of UGA in mRNAs which code for readthrough pro te ins by the suppression of UGA by normal Escherichia co l i tRNATrP. I t i s suggested tha t the na ture of the nucleot ide following a UGA codon determines whether the UGA s igna l s i n e f f i c i e n t l y or e f f i c i e n t l y the terminat ion of polypeptide chain syn thes i s: an A residue a t t h i s pos i t i on permits the UGA readthrough process