Poly (ADP-ribose) polymerases (PARPs) are enzymes that add ADP-ribose moieties to specific acceptor proteins. Best characterized are PARP-1 and PARP-2, which function as survival factors that modify nuclear proteins such as histones and topoisomerases during DNA damage signalling. Gilbert de Murcia and co-workers have now cloned and characterized a novel member of the PARP family, PARP-3, which might have a rather different function (see p. 1551). PARP-3 displays PARP activity in vitro, and its catalytic domain shares significant sequence similarity (61%) with PARP-1. The authors find that the protein localizes to centrosomes, where it associates with PARP-1. In contrast to PARP-1, however,PARP-3 is present only at daughter centrioles – and thus represents the first known marker protein for these structures. Murcia and co-workers show that overexpression of PARP-3 or its noncatalytic N-terminal domain causes cells to arrest at the G1/S transition of the cell cycle. This finding is particularly...

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