CELL CYCLE-DEPENDENT PHOSPHORYLATION OF NUCLEOPORINS AND NUCLEAR-POREMEMBRANE-PROTEIN GP210

During mitosis in higher eukaryotic cells, the nuclear envelope membra nes break down into distinct populations of vesicles and the proteins of the nuclear lamina and the nuclear pore complexes disperse in the c ytoplasm. Since phosphorylation can alter protein-protein interactions and membrane traffic, we have examined the cell cycle-dependent phosp horylation of nuclear pore complex proteins. Nonmembrane nucleoporins Nup153, Nup214, and Nup358 that are modified by O-linked N-acetylgluco samine and recognized by a monoclonal antibody were phosphorylated thr oughout the cell cycle and hyperphosphorylated during M phase. Pore me mbrane glycoprotein gp210, that has a cytoplasmic, carboxyl-terminal d omain facing the pore, was not phosphorylated in interphase but specif ically phosphorylated in mitosis. Mutant and wild-type fusion proteins containing the cytoplasmic domain of gp210 were phosphorylated in vit ro and their phosphopeptide maps compared to that of mitotic gp210. Th is analysis showed that Ser(1880) of gp210 was phosphorylated in mitos is, possibly by cyclin B-p34(cdc2) or a related kinase. Several nuclea r pore complex proteins are therefore differentially phosphorylated du ring mitosis when pore complexes disassemble and reassemble.