ASSOCIATION OF THE PLANT P34CDC2-LIKE PROTEIN WITH P13SUC1 - IMPLICATIONS FOR CONTROL OF CELL-DIVISION CYCLES IN PLANTS

The cdc2-like p34 protein of wheat is closely similar to the p34(cdc2) enzyme of yeasts and animals since both have binding affinity for p13(suc1) protein encoded by the fission yeast suc1 gene. In yeast p13(suc1) participates in modulation of p34(cdc2) activity and is necessary for completion of mitosis. Wheat p34 that was affinity purified on p13(suc1) contained the PSTAIR amino acid sequence that is present in all known p34(cdc2) homologues and it also had H1 histone protein kinase activity that was independent of calcium and cyclic AMP, which is characteristic of p34(cdc2) in vitro. Functional equivalence with the known cell cycle control protein supports our earlier proposition that the high level of this homologue in wheat leaf meristem is important in determining where cell division can occur and the capacity for resumption of cell division. The affinity of plant p34 for fission yeast p13(suc1) suggested that a similar association occurs in plants. We have detected a plant homologue of p13(suc1) using affinity-purified antibody raised against the fission yeast protein, in wheat, pea and Chlamydomonas. We conclude that the distribution of p13(suc1) homologue in plants is likely to be ubiquitous. The suc1 gene function in Schizosaccharomyces pombe is essential for mitosis, in which it is required for inactivation of p34(cdc2). We propose that association of plant p34 with p13(suc1) is similarly involved in plant mitosis.