Qualitative analysis of the abilities of various mutants to perform intrachromosomal recombination. Cells were streaked onto LB plates containing lactose and the indicator dye 2,3,5-triphenyltetrazolium chloride (TTC) and were incubated at 37°C for 48 h. The ability to form lac+ (white) papillae depends on intrachromosomal recombination events (54). Strains are as follows: JC13509 (uvrD+), SS3368 [del(uvrD-yigE)::cat], SS5704 (uvrD303), SS5450 (uvrD701), SS5987 (uvrD303,701), and SS5987 [del(recA)200::frt].