Variations among glyV-derived glycine tRNA suppressors of glutamic acid codons.

Glutamic acid codon suppressors in 18 isogenic strains of Escherichia coli have been further characterized as to map location, dominance, growth rates in various media, suppression of the GAG codon, and tRNA profiles after reversed-phase column chromatography. In general the evidence supports the conclusion that all of these suppressors are due to mutations in glyV55, the gene for a GGA/G-reading mutant form of glyV tRNA, and that they represent several different classes that may correspond to at least as many different nucleotide changes. Furthermore, 17 of the 18 suppressors can coexist in a haploid genome with a glyT suppressor that is devoid of GGA-reading ability. This result indicates the retention by those glyV suppressors of some ability to respond to GGA as well as the acquisition of the ability to read GAA, and suggests the possibility of "wobble" in the middle position of the anticodons of those tRNA's.