Characterization of p80, a novel nuclear and cytoplasmic protein in dinoflagellates

The presence of myosin in dinoflagellates was tested using an anti-Acantham oeba castellanii myosin II polyclonal antibody on the heterotrophic dinofla gellate Crypthecodinium cohnii Seligo. Western blots revealed the presence of a unique band of 80 kDa in total protein extracts and after immunoprecip itation. Expression of this 80 kDa protein appeared constant during the dif ferent phases of the cell cycle. In protein extracts from various other din oflagellates, this 80 kDa protein was defected only in the autotrophic spec ies Prorocentrum micans Ehr. Screening of a C. cohnii cDNA expression libra ry with this antibody revealed a cDNA coding for an amino acid sequence wit hout homology in the databases. However, particular regions were detected : - a polyglutamine repeat domain in the N-terminal part of the protein, - f our peptide sequences associated with GTP-binding sites, - a sequence with slight homology to the rod tail of Caenorhabditis elegans myosin II, - a se quence with homology to a human kinesin motor domain. Immunocytolocalizatio n performed on C. cohnii thin sections with a polyclonal antibody raised ag ainst the recombinant protein showed p80 to be present both within the nucl eus and in the cytoplasm. Labelling was widespread in the nucleoplasm and m ore concentrated at the periphery of the permanently condensed chromosomes. In the cytoplasm, labelling appeared in a punctate region close to the nuc leus and in the flagellum. Potential functions of this novel protein are di scussed.