The role of the CCA sequence of tRNA in the peptidyl transfer reaction.

Peptidyl transfer is a key step in the process of protein biosynthesis. To examine the role of the universal CCA terminal sequence of tRNA in the process of peptidyl transfer, various mutant transcripts of Escherichia coli valine tRNA were constructed. Peptidyl transferase activity, monitored by the 'fragment reaction' with a slight modification, was decreased by mutation at any one base of CCA. The effect of mutation was moderate in the UCA, CUA and CCG mutants. Replacement of A76 by a pyrimidine nucleotide, or replacement of either C74 or C75 by a purine nucleotide caused a marked decrease in the activity. These findings suggested that the universal CCA terminus of tRNA makes a functional interaction with ribosomal RNA by base-pairing.