Abstract

Sixty-two mutants of E. coli K-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 to leu , another group, val-r-B is closely linked to thr , and a third mutant, val-r-D57 , lies between leu and thr . Conjugation experiments showed that the remainder of the mutants could be divided into three groups, val-r-A, val-r-E and val-r-F on the basis of their different times of transfer from Vhf donors to val-s F − recipients. All the mutants are sensitive to 10,000 μg./ml. valine; val-r-B and val-r-D mutants are resistant up to 80 μg./ml. valine; val-r-C mutants are resistant up to 1000 μg./ml. valine, and val-r-A , val-r-E and val-r-F mutants up to 5000 μg./ml. The functional significance of the genetic locations of these groups is discussed.