A CDC2‐Related Kinase is Associated with Macronuclear DNA Synthesis in Paramecium tetraurelia

Abstract

ABSTRACT. Cell division in higher eukaryotes is mainly controlled by CDK (serine/threonine) protein kinases and by other components of these kinase complexes. Previously, we showed homologous kinases also occur in the ciate Paramecium tetraurelia. In this report, a polyclonal antibody was produced against a GST fusion protein which contained the N‐terminal third of the previously isolated CDC2FTA protein. It recognized a 36 kDa polypeptide on western blots and did not cross‐react with the related 34 kDa polypeptide. This 36 kDa polypeptide showed no affinity for yeast P13suc1 protein. The CDC2PTA level was invariant throughout the cell cycle and decreased slightly when cells entered stationary phase. Indirect immunofluorescence showed CDC2PTA localized in the macronucleus, but not in micronuclei. Native CDC2FTA was immunoprecipitated and the kinase activity was assayed using histone HI as substrate in elutriation synchronized samples. The kinase activity was high during the early stages of the cell cycle and reached a peak at 2.5 h after elutriation, which corresponds to the time of initiation of macronuclear DNA synthesis. This suggests CDC2PTA kinase may be associated with the regulation of macronuclear DNA synthesis. These results allow us to draw concrete comarisons for the first time between the role of CDK in ciliates and higher eukaryotes.