Tipper D J, Schmitt M J
Department of Molecular Genetics and Microbiology, University of Massachusetts Medical School, Worcester 01655.
Mol Microbiol. 1991 Oct;5(10):2331-8. doi: 10.1111/j.1365-2958.1991.tb02078.x.
The cytoplasmic L-A dsRNA virus of Saccharomyces cerevisiae consists of a 4.5 kb dsRNA and the two gene products it encodes; the capsid (cap) and at least one copy of the capsid-polymerase (cap-pol) fusion protein. Virion cap-pol catalyses transcription of the plus (sense)-strand; this is extruded from the virus and serves as messenger for synthesis of cap and cap-pol. Nascent cap-pol binds to a specific domain in the plus strand to initiate encapsidation and then catalyses minus-strand synthesis to complete the replication cycle. Products of at least three host genes are required for replication, and virus copy number is kept at tolerable levels by the SKI antivirus system. S. cerevisiae killer viruses are satellite dsRNAs that use a similar encapsidation domain to parasitize the L-A replication machinery. They encode precursors of secreted polypeptide toxins and immunity (specific resistance) determinants and are self-selecting. Three unique killer types, K1, K2 and K28, are currently recognized. They are distinguished by an absence of cross-immunity and by toxin properties and lethal mechanisms; while K1 and K2 toxins bind to cell-wall glucan and disrupt membrane functions, K28 toxin binds to mannoprotein and causes inhibition of DNA synthesis.
酿酒酵母的细胞质L-A双链RNA病毒由一段4.5 kb的双链RNA及其编码的两种基因产物组成；衣壳（cap）和至少一份衣壳-聚合酶（cap-pol）融合蛋白。病毒粒子cap-pol催化正（义）链的转录；正链从病毒中挤出，作为合成cap和cap-pol的信使。新生的cap-pol与正链中的一个特定结构域结合以启动衣壳化，然后催化负链合成以完成复制周期。复制需要至少三个宿主基因的产物，并且病毒拷贝数通过SKI抗病毒系统保持在可耐受水平。酿酒酵母杀伤病毒是卫星双链RNA，它们利用类似的衣壳化结构域寄生L-A复制机制。它们编码分泌型多肽毒素和免疫（特异性抗性）决定簇的前体，并且具有自我选择性。目前已识别出三种独特的杀伤类型，K1、K2和K28。它们的区别在于缺乏交叉免疫以及毒素特性和致死机制；K1和K2毒素与细胞壁葡聚糖结合并破坏膜功能，而K28毒素与甘露糖蛋白结合并导致DNA合成受到抑制。
