THE CARBOXYL-TERMINAL DOMAIN OF HUMAN POLY(ADP-RIBOSE) POLYMERASE - OVERPRODUCTION IN ESCHERICHIA-COLI, LARGE-SCALE PURIFICATION, AND CHARACTERIZATION

The cDNA encoding the carboxyl-terminal 40-kDa domain of human poly(AD P-ribose) polymerase was inserted into an expression vector. The recom binant protein was overproduced in Escherichia coli, and purified to h omogeneity. The 40-kDa domain had the same affinity (K(m)) for NAD+ as the full-length enzyme, expressed abortive NAD+ glycohydrolase activi ty, catalyzed the initiation, elongation, and branching of ADP-ribose polymers, but exhibited no DNA dependence. Its specific activity was a pproximately 500-fold lower than that of the whole enzyme activated by DNA strand breaks. Surprisingly, the carboxyl-terminal 40-kDa domain exhibited the processive mode of polymer attachment typical of full-le ngth poly(ADP-ribose) polymerase and was able to modify histones H1 an d H2B. Finally, the polymer sizes formed by the 40-kDa domain were inf luenced by histone H1.