Inactivation of bacteriophage lambda containing semiconserved alkylated deoxyribonucleic acid.

Immediate and delayed inactivation of ethylmethane sulfonate (EMS)-treated lambda phage were studied. Phage particles with one alkylated and one intact deoxyribonucleic acid (DNA) strand were obtained by allowing host-modified, EMS-treated phage to undergo one growth cycle in a nonmodifying host and selecting the progeny with semiconserved parental DNA on a restricting host. The results indicate that particles with one alkylated DNA strand are more sensitive to a second treatment with the alkylating agent. When incubated at 37 C, they are subject to inactivation at a rate which is smaller than that of phages containing two alkylated DNA strands. It appears that depurination events in one of the DNA strands of a phage particle are sufficient to cause death.