Abstract
The tRNAs specified by the wild type and amber suppressor alleles of the Escherichia coli supD gene have been identified, and their primary structures determined. The sequences differ by a single nucleotide in the middle of the anticodon. A CUA anticodon allows the suppressor tRNA to read the UAG stop codon; the CGA anticodon in the minor serine tRNA species from which the suppressor is derived is specific for the serine codon UCG.