Polypeptide Chain Initiation in Caulobacter crescentus without Initiation Factor IF-1

Two subspecies of initiation factor IF-2 have been isolated from ribosomal washes of Caulobacter crescentus and purified to homogeneity. Both factors, C-IF-2a and b, have the same functional properties and are interchangeable with Escherichia coli IF-2 for the formation of initiation complexes with either E. coli or C. crescentus ribosomes. The C. crescentus ribosomal wash contains no detectable IF-1 activity and the formation of initiation complexes with C. crescentus ribosomes has no requirement for added IF-1. With E. coli ribosomes C-IF-2a or b, or the crude C. crescentus ribosomal wash, must be supplemented with E. coli IF-1 for optimum initiation complex formation. IF-1 activity resides in C. crescentus salt-washed 30 S subunits.