The function, structure and regulation of E. coli peptide chain release factors

The termination of protein synthesis in Escherichia coli depends upon the soluble protein factors RF1 or RF2. RF1 catalyzes UAG and UAA dependent termination, while RF2 catalyzes UGA and UAA dependent termination. The proteins have been purified to homogeneity, their respective genes isolated, and their primary structures deduced from the DNA sequences. The sequences reveal considerable conserved homology, presumably reflecting functional similarities and a common ancestral origin. The RFs are encoded as single copy genes on the bacterial chromosome. RF2 exhibits autogenous regulation in an in vitro translation system. The mechanism of autoregulation appears to be an in-frame UGA stop codon that requires a 1+ frameshift for the continued synthesis of the protein. Frameshifting prior to the inframe stop codon occurs at a remarkably high frequency by an unknown mechanism. Future studies will be directed at understanding how RFs interact with the ribosomal components, and further defining the mechanism of RF2 frameshifting.