Bacterial peptide chain release factors: Conserved primary structure and possible frameshift regulation of release factor 2

Abstract

Escherichia coli peptide chain release factors are proteins that direct the termination of translation in response to specific peptide chain termination codons. The mechanisms of codon recognition and peptidyl-tRNA hydrolysis are unknown. We have characterized the genes encoding release factor 1 (RF-1) and release factor 2 (RF-2) to study the structure-function relationships of the proteins and their regulation in the bacterium. In this report, we present the gene structure of RF-1 and RF-2, and a partial peptide sequence of RF-2. RF-1 and RF-2 are highly homologous in their primary structure. In addition, an in-frame premature opal (UGA) termination codon is located within the RF-2 coding region at amino acid position 26. This region of the protein was sequenced by automated Edman degradation to confirm the predicted reading frame, and a second independent isolate of the RF-2 gene was identified and sequenced to confirm the DNA sequence. These results imply that a frameshift occurs prior to the premature termination codon, thus allowing for translation of RF-2 to be completed. This may represent a mechanism of translational control of RF-2 expression. An alternative possible means of translational regulation is discussed.