Mutant of the glutamine transfer RNA gene as UGA suppressor in Escherichia coli

A UGA suppressor derived from a glutamine tRNA gene of Escherichia coli K 12 was isolated and characterized. Phages carrying the suppressor su+2UGA could be obtained only from a hybrid transducing phage, h80cI857psu+2oc, but not from the original transducing phage λcI857psu+2oc. By DNA sequence analysis, it was found that the su+2 UGA suppressor obtained has two mutations; one is in the anticodon (TTA→TCA), as expected, and the other (C→T) is at the 7th position from the 3′ end of tRNA 2 Gln . The significance of these mutations and the lethal effect on phage λ of the increased amounts of UGA suppressor tRNAs are discussed.