Valine-resistant mutants ofEscherichia coliK-12

Abstract

Sixty-two mutants ofE. coliK-12 resistant to 40 μg./ml. valine were isolated from a sensitive strain. Transduction experiments using phage P1 showed that one group of these mutants,val-r-C, is closely linked toleu, another group,val-r-Bis closely linked tothr, and a third mutant,val-r-D57, lies betweenleuandthr. Conjugation experiments showed that the remainder of the mutants could be divided into three groups,val-r-A, val-r-Eandval-r-Fon the basis of their different times of transfer from Vhf donors toval-sF−recipients. All the mutants are sensitive to 10,000 μg./ml. valine;val-r-Bandval-r-Dmutants are resistant up to 80 μg./ml. valine;val-r-Cmutants are resistant up to 1000 μg./ml. valine, andval-r-A,val-r-Eandval-r-Fmutants up to 5000 μg./ml. The functional significance of the genetic locations of these groups is discussed.