Modified map positions for lac and the pro markers in Escherichia coli K-12.

Interrupted mating experiments were performed with Hfr strains H and C and three leu lac purE recipient strains derived from a common parent and carrying, respectively, the proA(-), proB(-), and proC(-) mutations. It was concluded that if leu is placed at 1.5 min and purE at 12 min from thr, the origin on the Taylor-Trotter map, lac is at about 7.5 min and the pro genes are at about 6.0, 6.6, and 8.4 min, respectively. Both conjugational and transductional data suggest that the strain carrying the proB(-) mutation also carries a second mutation close to the proA site which independently confers a Pro(-) phenotype. The times before the onset of transfer of chromosomal deoxyribonucleic acid by both Hfr strains B4 and B8 were approximately 3 min.