Studies on algal histones and histone-like proteins in dinoflagellates

Vita.In the search for the origin of the five histone types which occur in similar form in both higher plants and animals, we studied the chromosomal proteins of primitive eukaryotic organisms. Chromatin spreads made from isolated nuclei of the unicellular green alga Chlamydomonas reinhardtii showed the beaded fibers typical of eukaryotic polynucleosomes. Micrococcal nuclease digestions confirmed the presence of nucleosomes with a repeat length of 189 base pairs. Histones extracted from isolated nuclei were subjected to qualitative peptide mapping with V8 protease on SDS gels, fractionated by reverse phase high performance liquid chromatography (HPLC) and their amino acid compositions determined. C. reinhardtii was determined to have a full complement of the five histones with properties similar to those of higher plants and animals. The histones of the marine unicellular alga Olisthodiscus luteus were prepared from isolated nuclei, fractionated by HPLC, characterized by amino acid analysis, peptide mapping, and compared to calf thymus histones. Using the above criteria, we have identified the five major histones equivalent to those found in higher eukaryotes, with some differences in amino acid composition. Histones of the endosymbiont nuclei of the binucleate dinoflagellates Peridinium balticum and Peridinium foliaceum were prepared from isolated nuclei and analyzed by peptide mapping, amino acid composition, and two dimensional gel electrophoresis. The endosymbionts were found to have the normal complement of five major histones, with some differences between the two organisms. The histone-like basic nuclear proteins of the uninucleate dinoflagellate Crypthecodinium cohnii were extracted and fractionated by carboxymethyl cellulose chromatography and HPLC. Amino acid analysis and partial amino acid sequencing of some of the basic nuclear proteins, and a protein database search, revealed no homology with any known proteins, including histones of eukaryotes or histone-like proteins of prokaryotes. This work is of evolutionary interest because it is not presently known if the five major histones evolved separately, or share a common ancestral protein(s)