A PSTAIRE CDK-like protein localizes in nuclei and cytoplasm of Physarum polycephalum and functions in the mitosis.

CDKs play key roles in controlling cell cycle progression in all eukaryotes. In plants, multiple CDKs are present, among which the best characterized CDKs are PSTAIRE CDKs. In this study, we carried out Western blot, immunoelectron microscopy and antibody treatment with an anti-PSTAIRE monoclonal antibody to explore the subcellular localization and functions of PSTAIRE CDKs in Physarum polycephalum. The results of western blot and immunoelectron microscopy showed that in P. polycephalum, a PSTAIRE CDK-like protein was 34 kD in molecular weight and located in both nuclei and cytoplasm. In nuclei, the protein was mainly associated with chromosomes and nucleoli. The expression of the PSTAIRE CDK-like protein in both the plasmodia and nuclei showed little fluctuation through the whole cell cycle. When treated with an anti-PSTAIRE monoclonal antibody at early S phase, the cells were arrested in S phase, and the mitotic onset of P. polycephalum was blocked for about 1 h when treated at early G2 phase. Our data indicated that the PSTAIRE CDK- like protein has a direct bearing on the mitosis.