Schmitt M J, Tipper D J
Department of Molecular Genetics and Microbiology, University of Massachusetts Medical School, Worcester 01655.
Mol Cell Biol. 1990 Sep;10(9):4807-15. doi: 10.1128/mcb.10.9.4807-4815.1990.
The double-stranded RNA (dsRNA) viruses of Saccharomyces cerevisiae consist of 4.5-kilobase-pair (kb) L species and 1.7- to 2.1-kb M species, both found in cytoplasmic viruslike particles (VLPs). The L species encode their own capsid protein, and one (LA) has been shown to encode a putative capsid-polymerase fusion protein (cap-pol) that presumably provides VLPs with their transcriptase and replicase functions. The M1 and M2 dsRNAs encode the K1 and K2 toxins and specific immunity mechanisms. Maintenance of M1 and M2 is dependent on the presence of LA, which provides capsid and cap-pol for M dsRNA maintenance. Although a number of different S. cerevisiae killers have been described, only K1 and K2 have been studied in any detail. Their secreted polypeptide toxins disrupt cytoplasmic membrane functions in sensitive yeast cells. K28, named for the wine S. cerevisiae strain 28, appears to be unique; its toxin is unusually stable and disrupts DNA synthesis in sensitive cells. We have now demonstrated that 4.5-kb L28 and 2.1-kb M28 dsRNAs can be isolated from strain 28 in typical VLPs, that these VLPs are sufficient to confer K28 toxin and immunity phenotypes on transfected spheroplasts, and that the immunity of the transfectants is distinct from that of either M1 or M2. In vitro transcripts from the M28 VLPs show no cross-hybridization to denatured M1 or M2 dsRNAs, while L28 is an LA species competent for maintenance of M1. K28, encoded by M28, is thus the third unique killer system in S. cerevisiae to be clearly defined. It is now amenable to genetic analysis in standard laboratory strains.
酿酒酵母的双链RNA（dsRNA）病毒由4.5千碱基对（kb）的L型和1.7至2.1 kb的M型组成，二者均存在于细胞质中的病毒样颗粒（VLP）中。L型编码自身的衣壳蛋白，其中一种（LA）已被证明编码一种假定的衣壳 - 聚合酶融合蛋白（cap-pol），推测该蛋白为VLP提供转录酶和复制酶功能。M1和M2双链RNA编码K1和K2毒素以及特定的免疫机制。M1和M2的维持依赖于LA的存在，LA为M双链RNA的维持提供衣壳和cap-pol。尽管已经描述了许多不同的酿酒酵母杀手株，但只有K1和K2得到了详细研究。它们分泌的多肽毒素破坏敏感酵母细胞中的细胞质膜功能。以酿酒酵母葡萄酒菌株28命名的K28似乎是独特的；其毒素异常稳定，并破坏敏感细胞中的DNA合成。我们现在已经证明，可以从菌株28的典型VLP中分离出4.5 kb的L28和2.1 kb的M28双链RNA，这些VLP足以赋予转染的原生质球K28毒素和免疫表型，并且转染体的免疫性与M1或M2的免疫性不同。来自M28 VLP的体外转录本与变性的M1或M2双链RNA没有交叉杂交，而L28是一种能够维持M1的LA型。因此，由M28编码的K28是酿酒酵母中第三个被明确界定的独特杀手系统。现在它适合在标准实验室菌株中进行遗传分析。
