Nature of the repair of methyl methanesulfonate-induced damage in Bacillus subtilis.

A nuclease present in extracts of Bacillus subtilis inserts breaks in deoxyribonucleic acid (DNA) treated with the monofunctional alkylating agent, methyl methanesulfonate (MMS), but the nature of the sites within the alkylated macromolecule at which these breaks occur is not known. DNA extracted from B. subtilis cells that have recovered from MMS damage has lost its susceptibility to enzyme action. The recovery process is accompanied by some DNA breakdown and by the incorporation of thymidine. Some recovery from ultraviolet irradiation (UV) and MMS occurred in organisms starved for thymine or adenine, but UV recovery was stimulated by their addition. It is possible that MMS recovery proceeds by a process of excision and repair similar to, but not identical with, UV repair.