Catalytic Activities of Human Poly (ADP-Ribose) Polymerase after SDS-Page
Poly(ADP-ribose)polymerase is an eukaryotic enzyme, localized in the nucleus, which uses NAD as substrate to catalyze the ADP-ribosylation of the polymerase itself and of a variety of acceptor proteins (see Figure 1). Enzyme activity is dependent on the presence of DNA strand breaks (1) and is stimulated in vivo by DNA-damaging agents. Several lines of evidence indicate that poly(ADP-ribose) is implicated in different processes, such as DNA repair (2), cell differentiation (3) and sister chromatid exchange (4), all of which imply modifications of chromatin structure. The precise function of this enzyme is still much debated. Lehmann and coworkers postulated (5) that the polymerase reduces the steady-state level of breaks in the cellular DNA by stimulating the activity of DNA ligase II (6) or by altering the structure of chromatin so that DNA ligase can more easily join strand breaks (7). Olivera suggested that the interaction with DNA lesions results in poly(ADP-autoribosylation) of the enzyme, until repulsion between the activating DNA and the negatively charged polymer causes the dissociation of the enzyme from the chromatin (8). Recently, this group has demonstrated that DNA topoisomerase I from calf thymus is modified and inactivated by the poly(ADP-ribose)polymerase (9, 10).
KeywordsHeLa Cell Sister Chromatid Exchange Activity Band Dimethyl Sulfate Acceptor Protein
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