Dinoflagellates are a group of organisms which posses a number of traits that are unique among eukaryotes. Their unusual characteristics include the lack of histones and nucleosomes, an extra-nuclear spindle, and permanently condensed chromosomes. In order to accommodate these peculiar features, dinoflagellates must incorporate some special modifications to their cell cycle machinery....[ Read more ]

Dinoflagellates are a group of organisms which posses a number of traits that are unique among eukaryotes. Their unusual characteristics include the lack of histones and nucleosomes, an extra-nuclear spindle, and permanently condensed chromosomes. In order to accommodate these peculiar features, dinoflagellates must incorporate some special modifications to their cell cycle machinery.

The purpose of this investigation is to use the dinoflagellate as a model to study various cell cycle regulatory proteins, and to determine if the behavior of these proteins differs from that of other eukaryotes. This was accomplished through the use of various immunological approaches and cell staining techniques. It was observed that the dinoflagellate Cypthecodinium cohnii had several cyclin-like proteins, which exhibited a pattern of expression and degradation reminiscent of typical eukaryotic cyclins. Additionally, the cyclin-like polypeptides were shown to bind to the cell cycle protein Sucl. The binding partners of cyclins, the cyclin-dependent kinases (CDKs) were also present in C. cohnii. Two proteins of 34 and 46 kDa were observed in western blotting using antibodies targeting the conserved PSTAIRE motif. An increase in H1 histone kinase activity was also found to coincide with mitosis in synchronized cells.

The DNA replication protein PCNA was detected immunologically and had a nuclear localization, however, the size of the observed polypeptide was significantly larger than has been previously described. This difference may reflect the unusual cell cycle of the organism under investigation.