T-antigen interactions with chromatin and p53 during the cell cycle in extracts from Xenopus eggs

The role of SV40 large tumor T-antigen in replication of viral DNA is well established, but it is still unclear how T-antigen triggers cellular replic ation and cell transformation in non-permissive cells. Here, we used Xenopu s egg extracts which reproduce most nuclear events linked to the cell cycle in vitro to analyze its interaction with genomic chromatin during the cell cycle. We show that T-antigen associates with chromatin before the nuclear membrane formation, and further demonstrate that the nuclear membrane is n ot necessary for its impart into the nucleus. We show that the interaction of T-antigen with the endogenous chromatin does not occur at replication fo ci nor at RPA pre-replication centers. Immunoprecipitations as well as sucr ose gradient experiments, indicate that the endogenous pool of p53 interact s with T-antigen. In addition, a transient association of both proteins wit h the nuclear matrix is observed during the ongoing DNA synthesis. These da ta are discussed in view of the T-antigen and p53 activity during the cell cycle. J. Cell. Biochem. 75:288-299, 1999. (C) 1999 Wiley-Liss, Inc.