CELL-CYCLE REGULATION OF THE PRIMITIVE DINOFLAGELLATE CRYPTHECODINIUM-COHNII BIECHELER - EVIDENCE FOR THE PRESENCE OF AN HOMOLOG OF CYCLIN-B

Despite their early emergence in evolution, the protist dinoflagellate s present similarities in cell cycle regulation with higher eukaryotes and yeasts. Using antibody directed against the p56(cdc13) Of the fis sion yeast, we present evidence for the presence of a cyclin B homolog in the dinoflagellate Crypthecodinium cohnii. Biochemistry, immunoflu orescence and electron microscopy show the continuous presence of the cyclin B homolog during the C cohnii cell cycle progression. Cyclin B, which appears to be exclusively cytoplasmic, is associated with a spe cific H1 kinase activity more active in M phase.