Phase-Specific Polypeptides and Poly(A)+ RNAs during the Cell Cycle in Synchronous Cultures of Catharanthus roseus Cells

This study shows an overall analysis of gene expression during the cell cycle in synchronous suspension cultures of Catharanthus roseus cells. First, the cellular cytoplasmic proteins were fractionated by two-dimensional gel electrophoresis and visualized by staining with silver. Seventeen polypeptides showed qualitative or quantitative changes during the cell cycle. Second, the rates of synthesis of cytoplasmic proteins were also investigated by autoradiography by labeling cells with [(35)S]methionine at each phase of the cell cycle. The rates of synthesis of 13 polypeptides were found to vary during the cell cycle. The silverstained electrophoretic pattern of proteins in the G(2) phase in particular showed characteristic changes in levels of polypeptides, while the rates of synthesis of polypeptides synthesized during the G(2) phase did not show such phase-specific changes. This result suggests that posttranslational processing of polypeptides occurs during or prior to the G(2) phase. In the G(1) and S phases and during cytokinesis, several other polypeptides were specifically synthesized. Finally, the variation of mRNAs was analyzed from the autoradiograms of in vitro translation products of poly(A)(+) RNA isolated at each phase. Three poly(A)(+) RNAs increased in amount from the G(1) to the S phase and one poly (A)(+) RNA increased preferentially from the G(2) phase to cytokinesis.