Chlorella viruses.
Chlorella viruses or chloroviruses are large, icosahedral, plaque-forming, double-stranded-DNA-containing viruses that replicate in certain strains of the unicellular green alga Chlorella. DNA sequence analysis of the 330-kbp genome of Paramecium bursaria chlorella virus 1 (PBCV-1), the prototype of this virus family (Phycodnaviridae), predict approximately 366 protein-encoding genes and 11 tRNA genes. The predicted gene products of approximately 50% of these genes resemble proteins of known function, including many that are completely unexpected for a virus. In addition, the chlorella viruses have several features and encode many gene products that distinguish them from most viruses. These products include: (1) multiple DNA methyltransferases and DNA site-specific endonucleases, (2) the enzymes required to glycosylate their proteins and synthesize polysaccharides such as hyaluronan and chitin, (3) a virus-encoded K(+) channel (called Kcv) located in the internal membrane of the virions, (4) a SET domain containing protein (referred to as vSET) that dimethylates Lys27 in histone 3, and (5) PBCV-1 has three types of introns; a self-splicing intron, a spliceosomal processed intron, and a small tRNA intron. Accumulating evidence indicates that the chlorella viruses have a very long evolutionary history. This review mainly deals with research on the virion structure, genome rearrangements, gene expression, cell wall degradation, polysaccharide synthesis, and evolution of PBCV-1 as well as other related viruses.
Yamada
Takashi
T
Department of Molecular Biotechnology, Graduate School of Advanced Sciences of Matter, Hiroshima University, Higashi, Japan.
Onimatsu
Hideki
H
Van Etten
James L
JL
D001483:Base Sequence; D002473:Cell Wall / Q000378:metabolism; D002708:Chlorella / Q000821:virology*; D019143:Evolution, Molecular; D008969:Molecular Sequence Data; D017862:Phycodnaviridae / Q000235:genetics / Q000378:metabolism / Q000648:ultrastructure; D011134:Polysaccharides / Q000096:biosynthesis; D014764:Viral Proteins / Q000235:genetics / Q000378:metabolism; D014771:Virion / Q000378:metabolism
D011134:Polysaccharides; D014764:Viral Proteins