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 dinoflagellates present similarities in cell cycle regulation with higher eukaryotes and yeasts. Using antibody directed against the p56(cdc13) Of the fission yeast, we present evidence for the presence of a cyclin B homolog in the dinoflagellate Crypthecodinium cohnii. Biochemistry, immunofluorescence 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 specific H1 kinase activity more active in M phase.