Isolation of the major basic nuclear protein and its localization on chromosomes of the dinoflagellate, Oxyrrhis marina

Basic nuclear proteins were extracted from isolated nuclei of Oxyrrhis marina. The HPLC pattern of the extract showed a single major peak, which consisted of a major band with an apparent molecular mass of 23 kDa on an SDS-PAGE gel. We designated this protein as Np23 because of its apparent molecular mass. The amino acid composition of this protein revealed its extremely basic nature with a high lysine content. Polyclonal antibodies were raised against Np23. Immunofluorescence microscopy showed that Np23 was localized within the nucleus of dividing and non-dividing cells as well, and immuno-electron microscopy showed that the protein was localized only on chromosomes. These data established that Np23 is the major basic chromosome protein of Oxyrrhis marina.