LAMBDA PHAGE MUTANTS INSENSITIVE TO TEMPERATURE-SENSITIVE REPRESSOR .I. ISOLATION AND GENETIC ANALYSIS OF WEAK-VIRULENT MUTANTS

Weak-virulent mutants of temperate coli-phage λ were isolated which can grow on the λCI ts lysogen producing a temperature-sensitive repressor but which cannot grow on the wild type λ lysogen producing a normal repressor. Genetic analysis on the mutants shows that their weak-virulence is attributable to two mutations, one (virL) in the region between sus N213 and c47 and the other (virR) in the region between c1 and sus O8. Both mutations are located within the region of non-homology between λ and λimm434 phages. True virulent mutants which can grow on the wild type λ lysogen can be obtained easily from the weak-virulent mutant by an additional mutation, virC in a region very close to virR. The virulent mutants obtained are similar to the classical λvir mutant (Jacob and Wollman, 1954). The virL and virR mutations are probably operator mutations which render the genome insensitive to the λ repressor. © 1969 Springer-Verlag.