Wu L C, Fisher P A, Broach J R
J Biol Chem. 1987 Jan 15;262(2):883-91.
The Saccharomyces yeast plasmid, 2-micron circle, encodes a partitioning system that ensures equidistribution of plasmid molecules to both progeny following cell division. This system consists of two proteins encoded in plasmid genes REP1 and REP2 and a cis-active noncoding locus, designated REP3. We have raised antibodies against a REP1 beta-galactosidase fusion protein and used them to identify the authentic REP1 protein in plasmid-bearing yeast cells. We find that REP1 protein is located exclusively in the nucleus and co-purifies with a karyoskeletal protein subfraction operationally and morphologically equivalent to the nuclear matrix-pore complex-lamina fraction of higher cells. The carboxyl half of the REP1 protein exhibits strong sequence homology to myosin heavy chain, vimentin, and nuclear lamins A and C, indicating a fibrous structure for the protein. From these observations, we suggest that REP1 protein may promote plasmid partitioning by intercalating into the nuclear lamina of the host cell to provide dispersed anchorage sites for attachment of plasmid molecules.
酿酒酵母质粒2-微米环编码一种分配系统，该系统可确保质粒分子在细胞分裂后均等地分配到两个子代细胞中。该系统由质粒基因REP1和REP2编码的两种蛋白质以及一个顺式作用的非编码位点REP3组成。我们制备了针对REP1β-半乳糖苷酶融合蛋白的抗体，并使用它们来鉴定携带质粒的酵母细胞中的天然REP1蛋白。我们发现REP1蛋白仅位于细胞核中，并与一种核骨架蛋白亚组分共纯化，该亚组分在功能和形态上与高等细胞的核基质-核孔复合体-核纤层组分相当。REP1蛋白的羧基末端与肌球蛋白重链、波形蛋白以及核纤层蛋白A和C具有很强的序列同源性，表明该蛋白具有纤维结构。基于这些观察结果，我们推测REP1蛋白可能通过插入宿主细胞的核纤层中，为质粒分子的附着提供分散的锚定位点，从而促进质粒的分配。
