A bipartite nuclear localization signal is required for p53 nuclear importregulated by a carboxyl-terminal domain

Abnormal p53 cellular localization has been considered to be one of the mec hanisms that could inactivate p53 function. To understand the regulation of p53 cellular trafficking, we have previously identified two p53 domains in volved in its localization. A basic domain, Lys(305)-Arg(306), is required for p53 nuclear import, and a carboxyl-terminal domain, namely the cytoplas mic sequestration domain (CSD) from residues 326-355, could block the nucle ar import of Lys(305) Or Arg(306) mutated p53. To characterize further the function of these two domains, we demonstrate in this report that the previ ously described major nuclear localization signal works together with Lys(3 05)-Arg(306) to form a bipartite and functional nuclear localization sequen ce (NLS) for p53 nuclear import. The CSD could block the binding of p53 to the NLS receptor, importin alpha, and reduce the efficiency of p53 nuclear import in MCF-7, H1299, and Saos-2 cells. The blocking effect of the CSD is not due to the enhancement of nuclear export or oligomerization of the p53 . These results indicate that the CSD can regulate p53 nuclear import by co ntrolling access of the NLS to importin rw binding.