PLASMID HYPERRECOMBINATION IS TYPICAL FOR ESCHERICHIA-COLI HYPERRESISTANT STRAINS

Intraplasmid recombination frequency was assessed in several Escherich ia coli K12 strains by the kinetic bioluminescence method. Enhanced pl asmid recombination was observed in two mutant E. coli K12 strains, wh ich were hyperresistant to DNA-damaging agents, gamma-rays, and photos ensibilizer 8-methoxypsoralen. Plasmid recombination frequency per one generation (P) was calculated. In mutant strains, this value was show n to exceed that in control isogenic strains with a standard resistanc e approximately by a factor of 15. Enhanced constitutive synthesis of specific proteins such as heat-shock proteins in Gam(r)444 and a 55-kD a protein in SA270 in hyperresistant mutant strains is assumed to prom ote activity of the recombinational RecF pathway system.