The histones of the endosymbiont alga of Peridinium balticum (Dinophyceae)

CHARACTERIZATION OF GYMNODINIUM MIKIMOTOI (DINOPHYCEAE) NUCLEI AND IDENTIFICATION OF THE MAJOR HISTONE-LIKE PROTEIN, HGm

A simple and rapid method for isolation of nuclei from Gymnodinium mikimotoi Miyake et Kominami ex Oda is described along with chemical characterization of the nuclei. The isolated nuclei were completely free of whole cells, 99.96% free of cytoplasmic contamination, and were collected with a yield of 40% from harvested whole cells. Each nucleus contained 47 pg of DNA and the ratio of DNA to acid-soluble proteins to acid-insoluble proteins was 1:0.25:1.21, respectively. SDS electrophoresis of acid-extracted proteins showed one histone-like protein, which we termed HGm, with an apparent molecular mass of 12 kDa. V8 protease digestion analysis of HGm, the histone-like protein from Crypthecodinium cohnii (HCc), and two histone-like proteins from Gymnodinium dorsum, showed that the HGm digestion pattern was more similar to that of HCc than to that of either of the G. dorsum histone-like proteins.

Analysis of lysine-rich histones from the unicellular green alga Chlamydomonas reinhardtii

The H1 histones of the unicellular green alga Chlamydomonas reinhardtii were extracted from isolated nuclei, fractionated by high performance liquid chromatography, and analyzed by two-dimensional electrophoresis, peptide mapping, and N-terminal sequencing. Sodium dodecyl sulfate polyacrylamide gel electrophoresis of 5% perchloric acid extracts of isolated C. reinhardtii nuclei revealed two H1 proteins (H1A and H1B). Two-dimensional gel analysis did not reveal heterogeneity of either algal H1 protein, but did detect differences in the hydrophobic amino acid content of the C. reinhardtii H1A and H1B. Digestion of H1A and H1B with V8 protease revealed two distinctly different peptide maps. C. reinhardtii H1 peptide maps were not at all similar to those of Pisum H1, but algal and pea H2B peptide maps did show some peptides in common. Seventeen amino acid residues were obtained from C. reinhardtii H1A amino terminal sequencing, while the H1B N-terminus was blocked. A search of protein data bases revealed no sequence homology of the H1A N-terminus with any known protein. Chlamydomonas histones fractionated by high performance liquid chromatography revealed minor components (histone variants) for H2A and H2B. The amino acid composition of Chlamydomonas lysine-rich histones was compared to those of various other unicellular algae.

Ribosomal RNA analysis indicates a benthic pennate diatom ancestry for the endosymbionts of the dinoflagellates Peridinium foliaceum and Peridinium balticum (Pyrrhophyta)

The establishment of chloroplasts as cellular organelles in the dinoflagellate, heterokont (stramenopile), haptophyte, and cryptophyte algae is widely accepted to have been the result of secondary endosymbiotic events, that is, the uptake of a photosynthetic eukaryote by a phagotrophic eukaryote. However, the circumstances that promote such associations between two phylogenetically distinct organisms and result in the integration of their genomes to form a single functional photosynthetic cell is unclear. The dinoflagellates Peridinium foliaceum and Peridinium balticum are unusual in that each contains a membrane-bound eukaryotic heterokont endosymbiont. These symbioses have been interpreted, through data derived from ultrastructural and biochemical investigations, to represent an intermediate stage of secondary endosymbiotic chloroplast acquisition. In this study we have examined the phylogenetic origin of the P. foliaceum and P. balticum heterokont endosymbionts through analysis of their nuclear small subunit ribosomal RNA genes. Our analyses clearly demonstrate both endosymbionts are pennate diatoms belonging to the family Bacillariaceae. Since members of the Bacillariaceae are usually benthic, living on shallow marine sediments, the manner in which establishment of a symbiosis between a planktonic flagellated dinoflagellate and a bottom-dwelling diatom is discussed. In particular, specific environmentally-associated life strategy stages of the host and symbiont, coupled with diatom food preferences by the dinoflagellate, may have been vital to the formation of this association.

Molecular cloning and immunolocalization of two variants of the major basic nuclear protein (HCc) from the histone-less eukaryote Crypthecodinium cohnii (Pyrrhophyta)

Two clones that encode variants (HCc1 and HCc2) of the major basic nuclear protein of the dinoflagellate Crypthecodinium cohnii, were identified by immunoscreening of a cDNA expression library. The first clone carries a full-length cDNA with an open reading frame (HCc1) encoding 113 amino acids. The cDNA from the second clone lacks some of the 5' end, and the coding sequence is only 102 residues. The two proteins display 77% sequence similarity and their NH2-ends are homologous to the NH2-peptide of the HCc protein determined by P. Rizzo. The amino acid composition, which confirms the basic nature of lysine-rich HCc proteins, differs markedly from other known DNA-binding proteins such as histones, HMGs or prokaryotic histone-like proteins. No convincing homology was found with other proteins. HCc antigens were localized on C. cohnii by immunofluorescence, and by electron microscopy (EM) with immunogold labelling. HCc proteins are mainly detected at the periphery of the permanently condensed chromosomes, where active chromatin is located, as well as in the nucleolar organizing region (NOR). This suggests that these basic, non-histone proteins, with a moderate affinity for DNA, are involved at some level in the regulation of gene expression.

Analysis of Chlamydomonas reinhardtii histones and chromatin

Chromatin spreads made from isolated nuclei of the unicellular green alga Chlamydomonas reinhardtii show the beaded fibers typical of eukaryotic polynucleosomes. Micrococcal nuclease digestions confirmed the presence of nucleosomes with a repeat length of 189 base pairs, essentially the same as typical mammalian cells. Basic nuclear proteins extracted from isolated nuclei or chromatin with 1 M calcium chloride and 0.3 M hydrochloric acid are resolved into seven major components by electrophoresis in the presence of sodium dodecyl sulfate (SDS). These seven components were subjected to qualitative peptide mapping with V8 protease on SDS gels for comparison with the major histone components of calf thymus. Finally, the C. reinhardtii basic nuclear proteins were fractionated by reversed phase high performance liquid chromatography and their amino acid composition determined. From these studies, we conclude that C. reinhardtii has a full complement of the five histones with properties very similar to those of both higher animals and higher plants.