Variations in some molecular events during the early phases of the Reuber H 35 cell cycle. II.-Chromatin protein phosphorylation and protein kinases.
Reuber H 35 hepatoma cells were synchronized by transfer in a serum free medium. Growth was re-initiated by addition of serum. Under these conditions DNA synthesis exhibited a maximum after 24 hours. Chromatin non-histone proteins prepared from cells at various phases of the cell cycle were incubated with [gamma-32P] ATP and the radioactive pattern of protein bound 32P was analysed by electrophoresis on polyacrylamide gels. No radioactive peak was observed in G0. Several peaks appeared 3 hours after the addition of serum. The radioactivity progressively increased until the cells reached the S phase. When most of the cells were in the S phase the radioactivity strongly decreased. Chromatin protein kinase activities were found to increase in late G1 and continued to increase in the S phase. The increase was 65% when phosvitin was the substrate, 100% with casein and histone H1. It is suggested that chromatin phosphorylated proteins could be involved in the mechanism which initiates DNA synthesis in G1 phase cells.
D000818:Animals; D002453:Cell Cycle; D002460:Cell Line; D002868:Chromosomal Proteins, Non-Histone / Q000378:metabolism*; D008114:Liver Neoplasms, Experimental / Q000503:physiopathology; D010766:Phosphorylation; D011494:Protein Kinases / Q000378:metabolism*
D002868:Chromosomal Proteins, Non-Histone; D011494:Protein Kinases