The enzyme poly(ADP-ribose)polymerase (PARP) has been implicated in several cellular processes by the demonstration of ADP-ribosylation of proteins which play a role in cellular repair of DNA damage, response to ionizing radiation and apoptosis. In addition, ADP-ribosylation has been shown to play a role in cell cycle progression. To investigate the role of ADP-ribosylation in cell cycle progression, we have synchronized human squamous carcinoma cells (SQ-20B) and examined the changes in the pattern of ADP-ribosylation of proteins through the stages of the cell cycle. Moreover, synchronized SQ-20B cells were irradiated to determine the effects of irradiation on the patterns of ADP-ribosylation through the cell cycle phases. These studies showed the ADP-ribosylation of 3 specific proteins (70, 68 and 40 kDa) to change through the cell cycle. Furthermore, ionizing radiation altered the ADP-ribosylation patterns of these 3 proteins. Using a double antibody method, we determined that cyclins A, B1 and D1, cdc2 and PCNA are not modified by ADP-ribosylation.

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