MOLECULAR-CLONING OF A MURINE CDNA-ENCODING A NOVEL PROTEIN, P38-2G4,WHICH VARIES WITH THE CELL-CYCLE

Proliferating cells express genes active in cell cycle control. The mo dulation of control genes and factors are required to maintain critica l cell cycle activities. We used a set of monoclonal antibodies prepar ed against DNA-binding proteins from Ehrlich ascites tumor cells in im munofluorescent microscopy to screen for proteins showing cell cycle-s pecific staining patterns. Here, we report cloning and characterizing of a novel mitogen-inducible gene from murine macrophages that predict s a cell cycle-specifically modulated nuclear protein of 38 kDa, desig nated p38-2G4. p38-2G4 displayed a speckled pattern of varying fluores cence intensity confined to the nucleus, but sparing the nucleoli. Str ongly stained granules were observed between GT and mid S phase, follo wed by a less abundant punctated arrangement toward the end of S phase , and negative fluorescence at the S/G2 transition. Thereafter, the nu clear staining reappeared. Additionally, p38-2G4 expression vanished i n GO-arrested cells and was restored after release from growth arrest. p38-2G4 conserved in vertebrates by means of immunofluorescence data contains a number of putative phosphorylation sites, a cryptic nuclear localization signal, and an amphipathic helical domain. Our cDNA and its deduced amino acid sequence is related to a Schizosaccharomyces po mbe gene encoding a 42-kDa protein that associates with curved DNA, su ggesting that we have cloned the murine homologue of the S. pombe gene which defines a novel cell cycle-specifically modified and proliferat ion-associated nuclear protein in mammals. (C) Academic Press, Inc.