DNA repair patch size measurements with nucleosomal DNA.

A modified method for measuring DNA repair patch sizes by the bromodeoxyuridine buoyant density shift method is presented. This method involves the digestion of total chromatin by Staphylococcal nuclease to produce small DNA fragments with a very homogeneous size distribution. Using this method to measure the size of repair patches following treatment with u.v.-light or dimethyl sulfate, a calculated incorporation of 40 nucleotides was obtained. This value is identical to previously published patch size estimations obtained by the buoyant density shift method with sonically produced DNA fragments. It is also in close agreement with values recently obtained by the bromodeoxyuridine photolysis method. Taken together, these independent results obtained with a variety of DNA damaging agents suggest that excision repair patch size is independent of the damaging agent.