COMPARATIVE-STUDIES OF SYNTHESIS, PHOSPHORYLATION, DNA-BINDING AND PROTEOLYTIC CHARACTERISTICS OF A NOVEL PROTEIN DURING PHASES OF THE MOUSE SPLEEN-CELL CYCLE

1. Cultured mouse spleen cells were exposed to the mitogen Concanavalin A followed by isoproterenol, and nuclei were electronically sorted from seven partitions of the cell cycle. 2. Several nuclear proteins, including stress proteins, which were cell-cycle-stage specific, were elicited by isoproterenol as determined by micro-electrophoresis and fluorography. 3. Two novel S-phase proteins (X0 and X') demonstrated differing synthesis and phosphorylation patterns during the cell-cycle phases. 4. X' showed DNA binding characteristics and proteolytic properties (hydrolyzing X0 or beta-galactosidase); both proteins were cell-cycle regulated.