Mutations in the amino-terminal domain of the human poly(ADP-ribose) polymerase that affect its catalytic activity but not its DNA binding capacity

Poly-ADP ribosylation of nuclear proteins is activated when poly(ADP-ribose) polymerase (PARP), a nuclear zinc-finger enzyme, binds to single-strand DNA breaks, To understand how the signal emerging from its DNA-binding domain (DBD) bound to such breaks is transduced to its catalytic domain, the structure-function relationship of the DBD was investigated, We have used mutagenesis by the polymerase chain reaction (PCR) to generate a random library of PARP mutants, In this work, we describe the identification of catalytically inactive mutants bearing single point mutations, located outside the two zinc fingers in the DBD, that have conserved their full capacity to bind DNA. The results obtained demonstrate that the DNA-dependent activation of PARP requires not only a capacity to bind DNA but also a number of crucial residues to maintain a conformation of the domain necessary to transfer an 'activation signal' to the catalytic domain.