Poly(ADP-ribose) polymerase can bind melphalan damaged DNA

As a means of identifying damage recognition proteins involved in repair of nitrogen mustard lesions in chronic lymphocytic leukemia, we performed Southwestern analysis using a probe damaged with melphalan and protein extracts from chronic lymphocytic leukemia patients. We detected proteins with molecular weights of 116,000, 66,000, and 64,000 which bound the damaged probe with a higher specificity than the undamaged probe. The M(r) 66,000 and 64,000 proteins were determined to be degradation products of the M(r) 116,000 protein. The M(r) 116,000 protein was identified as poly(ADP-ribose) polymerase. The use of methoxyamine, an inhibitor of DNA strand breakage following depurination, significantly reduced binding of the melphalan damaged probe to poly(ADP-ribose) polymerase. Following depletion of poly(ADP-ribose) polymerase from the cell extracts, no other binding activity was discovered. Thus, poly(ADP-ribose) polymerase is the only demonstrable protein in chronic lymphocytic leukemia cells which can bind to a DNA probe damaged with melphalan.