Production of single-strand breaks in covalent circular lambda phage DNA in superinfected lysogens by monoalkylating agents and the joining of broken DNA strands.
Fast sedimenting, double-stranded, covalent circular lambda phage DNA in superinfected lysogens of Escherichia coli is converted to notched circular DNA, sedimenting slowly in alkaline sucrose gradients, by methylmethane sulfonate (MMS) treatment during incubation at 37 degrees . During further incubation after removal of the MMS, the slow sedimenting DNA reverts to the fast sedimenting structure. Covalent circular DNA, phenol extracted from superinfected lysogens and exposed to MMS, ethylmethane sulfonate, or 2-chloroethyl ethyl sulfide requires the presence of a heat-labile factor from extracts of E. coli for the breaks to appear. The cleavage of alkylated covalent circular DNA in vivo and the subsequent rejoining of the broken DNA strands to produce reconstructed covalent circular DNA may reflect the action of an excision-like repair process which is under different genetic control from that of pyrimidine dimer excision.
Boyce
R P
RP
Radiobiology Laboratories, Yale University School of Medicine, New Haven, Connecticut 06510, USA.
Farley
J W
JW