Cyclins in a dinoflagellate cell cycle

The dinoflagellates are distinct among eukaryotes in having an extranuclear spindle and permanently condensed chromosomes. These cytologic features implicate special adaptations to the molecular mechanisms of cell cycle control. We have demonstrated the presence of cyclin-box-containing polypeptides in dinoflagellates by using peptide-generated antibodies. We identified four major cyclin-box-containing polypeptides. The cell cycle dynamics of these polypeptides were also investigated in synchronized populations, using a newly developed method. Of the four major cyclin-box-containing polypeptides detected, a tripler with apparent molecular weight of 75 kDa did not change appreciably during the cell cycle. For two other cyclin-box-containing polypeptides with apparent molecular weights of 50 and 65 kDa, we observed an early expression in the cell cycle, with the level accumulating and eventually being degraded on the exit of mitosis. At least one cyclin-box-containing polypeptide (50 kDa) was also observed in a protein complex bound to p13(suc1) beads. The bound complex had associated histone kinase activity. Variation of this activity corresponded well with the periodic expression of the 50-kDa cyclin-box-containing polypeptide during the cell cycle of Crypthecodinium cohnii. This demonstrates the presence of cyclins and cyclin-dependent kinases in dinoflagellates.