Properties of peptide chain release factor 2 from Streptomyces coelicolor A3(2): conserved primary structure but no frameshift regulation.

A gene was cloned from Streptomyces coelicolor A3(2). It encodes a protein of 368 amino acid residues with a high degree of similarity to prokaryotic release factor 2. However, it has neither an internal stop codon nor the Shine-Dalgarno-like sequence immediately upstream of the assumed frameshift position. The gene is expressed and functional in Escherichia coli as peptide chain release factor 2. The transcription start site is at or adjacent to the translational start site. The size of the mRNA detected by hybridization suggests that the gene (prfB) is monocistronic in S. coelicolor A3(2). However, about 80 bp upstream of the gene there is an operon which is composed of two genes encoding eukaryotic-type serine/threonine kinases.