General method for the isolation of conditional lethal mutants in any required region of the virus genome: its application to the 'semi-essential' region of phage Mu.

A general method is presented that enables viral mutants to be isolated in any required region of their genome. An application of the method is reported relating to the isolation of conditional lethal mutants in the "semi-essential' region of phage Mu. Some properties are described of one mutant found in this way, Mucts62SEEam8 Apl, which is typical of a class of mutants that were isolated.