Van Etten J L, Meints R H
Department of Plant Pathology, University of Nebraska, Lincoln 68583-0722, USA.
Annu Rev Microbiol. 1999;53:447-94. doi: 10.1146/annurev.micro.53.1.447.
Paramecium bursaria chlorella virus (PBCV-1) is the prototype of a family of large, icosahedral, plaque-forming, double-stranded-DNA-containing viruses that replicate in certain unicellular, eukaryotic chlorella-like green algae. DNA sequence analysis of its 330, 742-bp genome leads to the prediction that this phycodnavirus has 376 protein-encoding genes and 10 transfer RNA genes. The predicted gene products of approximately 40% of these genes resemble proteins of known function. The chlorella viruses have other features that distinguish them from most viruses, in addition to their large genome size. These features include the following: (a) The viruses encode multiple DNA methyltransferases and DNA site-specific endonucleases; (b) PBCV-1 encodes at least part, if not the entire machinery to glycosylate its proteins; (c) PBCV-1 has at least two types of introns--a self-splicing intron in a transcription factor-like gene and a splicesomal processed type of intron in its DNA polymerase gene. Unlike the chlorella viruses, large double-stranded-DNA-containing viruses that infect marine, filamentous brown algae have a circular genome and a lysogenic phase in their life cycle.
草履虫小球藻病毒（PBCV-1）是一类大型、二十面体、能形成噬菌斑、含有双链DNA的病毒家族的原型，这类病毒在某些单细胞、真核的小球藻样绿藻中复制。对其330,742碱基对基因组的DNA序列分析表明，这种藻DNA病毒有376个蛋白质编码基因和10个转运RNA基因。这些基因中约40%的预测基因产物类似于已知功能的蛋白质。除了基因组庞大外，小球藻病毒还有其他一些使其有别于大多数病毒的特征。这些特征包括：（a）病毒编码多种DNA甲基转移酶和DNA位点特异性内切酶；（b）PBCV-1至少编码了其蛋白质糖基化所需机制的一部分，如果不是全部的话；（c）PBCV-1至少有两种类型的内含子——一种在类转录因子基因中的自我剪接内含子和一种在其DNA聚合酶基因中的剪接体加工型内含子。与小球藻病毒不同，感染海洋丝状褐藻的大型含双链DNA病毒有一个环状基因组，并且在其生命周期中有一个溶原阶段。
