Isolation of rec- mutants from an F-prime merodiploid strain of Escherichia coli K-12.

This paper describes a method of screening mutagenised populations of an E. coli galA/galB F- prime merodiploid for mutants defective in recombination. The method relies on scoring colonies on Eosin-Methylene Blue agar that have fewer than normal numbers of Gal+ papillae. With a suitable choice of gal- mutations most of the papillae arise by recombination and some of those colonies with less than normal numbers prove to be defective in some aspect of recombination or DNA repair. In addition to strains carrying mutations that can be ascribed to known loci, several novel mutant phenotypes were identified.