Reassociation of human lymphoblastoid cell DNA repair replicated following methyl methanesulfonate treatment

The reassociation rates of repair replicated DNA of two human lymphoblastoid cell lines, the WIL₂-A3 'normal' line and the RAJI line of Burkitt's lymphoma, were examined using the DNA/DNA 'C₀t' hybridization technique. The cells were treated with methyl methanesulfonate (MMS), an alkylating agent and mutagen, to induce the repair. The incorporated repair replication radioactivity in highly repetitive sequences of WIL₂-A3 cell DNA reassociates as expected for a randomly distributed incorporation. The reassociation of repair radioactivity in sequences of fewer numbers of copies, however, is less than expected for a random distribution. It is less than that occurring for semiconservatively synthesized DNA of WIL₂-A3 cells co-incubated with the repair labeled DNA as an internal control. The observed difference could be due to an over-representation of repair replication radioactivity in DNA sequences with fewer copies. It is unlikely to be due to residual alkali labile damage resulting from MMS treatment, since a similar difference was not observed when semiconservatively labeled DNA from cells which had been treated with MMS for the same time and at the same concentration as in the repair experiments was substituted for repair replicated DNA in the reassociation reactions. Other possible causes of the apparent difference in the reassociation rates observed are discussed.