HELICASE-II (UVRD) DETERMINES THE SOS-INDUCED PLASMID HYPERRECOMBINATION IN ESCHERICHIA-COLI

Using a kinetic bioluminescence method, the frequency of intraplasmid recombination was measured in a number of Escherichia coil strains. Co nsiderable enhancement of recombination (hyper-rec) was shown in the S C30 recA730 strain displaying constitutive synthesis of genes of the S OS regulon: the frequency of recombinations per generation (P) exceede d that for the control strain WP2 by an order of magnitude. A uvrD3 de letion in the SC30 strain cancels the phenomenon of plasmid hyperrecom bination. An elevated concentration of helicase II (uvrD gene) in SOS- induced cells may promote DNA unwinding. Thus, helicase II (UvrD) dete rmines SOS-induced hyperrecombination of plasmids.