[General method for selecting mutations in bacterial and phage genes essential for the development of bacteriophage mu]. / Obshchii metod otbora mutatsii v bakterial'nykh i fagovykh genakh, sushchestvennykh dlia razvitiia bakteriogaga Mu.

ABSTRACT

A method has been developed for a relatively easy selection of bacterial mutations, either inhibiting or promoting Mu growth, and of various mutations in the genome of the Mu phage itself. Spontaneous or induced mutations inhibiting Mu growth are tested in a bacterial strain carrying a Mucts62 prophage in the chromosome and a defective Muc+ prophage within an unstable and frequently eliminated plasmid (the "operational" strain). The cells of such a strain form colonies at 43 degrees C owing to the domination of the c+ allele, though a portion of the cells in a growing colony lose the plasmid with the Muc+ gene and die, dut to the induction of the Mucts prophage. In this case, a large number of phage particles are produced which cause cell lysis during the growth of a colony of the "operational" strain on a Mu-sensitive Escherichia coli lawn. The absence of a lysis zone around a colony of the "operational" strain would indicate a clone that is unable to produce viable Mu particles, as a result of a mutation in the bacterial or the phage genome. The situation is reverse when a strain incapable of maintaining Mu growth is used as the "operational" strain. Clones are tested for the ability to produce Mu on colour indicator media where the "operational" cells form coloured colonies and the tester cells form a colourless lawn. The method has been proved effective in a study conducted to test the use of Mu-lambda-Mu structures with defective lambda prophages flanked by identically oriented Mu genomes for selecting deletion mutants of Mu.