A mutant which reinitiates the polypeptide chain after chain termination

Abstract

A mutation, x, in the rII B cistron permits reinitiation of polypeptide synthesis after chain termination. Mutants containing this starter are isolated as base analogue-induced revertants of doubles containing an ochre or amber mutant and a (+) phase-shift mutant. Evidence is provided that such mutants synthesize two polypeptide chains. The starter is initiated in the (−) frame and requires a (+) phase shift on its right to compensate it. Chain termination is obligatory for activation of the starter, but can occur either to its left or its right. Restarting is independent of the phase between the terminator and starter, as shown by altering the phase of termination and by inserting phase-shift mutants between the terminator and starter.