Identification of the mutations in the prfB gene of Escherichia coli K12, which confer UGA suppressor activity.

By DNA sequencing and gene dissection, it has been revealed that Su+UGA#11, the mutant prfB of E. coli (Chang et al., 1990) has a double mutation compared with the wild-type LS653: one is a base substitution from T to C at the codon 63 and the other is from G to A at the codon 79. Both mutations cause amino acid substitution, Leu63----Phe63 (L63F) and Asp79----Gly79 (D79G), and are necessary to confer the efficient UGA suppressor activity.