S. cerevisiae Cells Can Grow without the Pds5 Cohesin Subunit.
S. cerevisiae Cells Can Grow without the Pds5 Cohesin Subunit.
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作者：
在DNA复制过程中，新产生的姐妹染色单体保持在一起，直到它们在后期分离。在所有真核生物中，cohesin复合物负责产生和维持姐妹染色单体凝聚（SCC）。在酿酒酵母细胞中，粘附素由两个细长的蛋白质Smc 1和Smc 3组成，由Kleisin Mcd 1/Scc 1桥接。后者还充当另外三种蛋白质Scc 3/Irr 1、Wpl 1/Rad 61和Pds 5的支架。虽然HEAT重复蛋白Pds 5是凝聚力所必需的，但其确切功能仍有争议。缺失编码PCNA卸载器的ELG 1基因，可以部分抑制温度敏感性<$5 -1等位基因，但不能完全缺失PDS 5。我们对高拷贝数抑制基因和自发产生的突变体进行了遗传筛选，使一株5 Δ elg 1 Δ菌株得以存活。我们的研究结果表明，细胞在Pds 5缺失的情况下仍然存活，前提是Mcd 1水平升高（这可能是由于编码G1细胞周期蛋白的CLN 2基因突变所致），以及染色质上SUMO修饰的PCNA水平升高（由elg 1 Δ突变体中缺乏PCNA卸载引起）。升高的SUMO-PCNA水平增加了Srs 2解旋酶的募集，Srs 2解旋酶将Rad 51分子从移动叉中驱逐，产生单链DNA（ssDNA）区域，其作为增加的粘附素加载和SCC建立的位点。因此，我们的研究结果描绘了一个双重的作用，Pds 5在保护的粘附环和相互作用的DNA复制机器。
During DNA replication, the newly created sister chromatids are held together until their separation at anaphase. The cohesin complex is in charge of creating and maintaining sister chromatid cohesion (SCC) in all eukaryotes. In Saccharomyces cerevisiae cells, cohesin is composed of two elongated proteins, Smc1 and Smc3, bridged by the kleisin Mcd1/Scc1. The latter also acts as a scaffold for three additional proteins, Scc3/Irr1, Wpl1/Rad61, and Pds5. Although the HEAT-repeat protein Pds5 is essential for cohesion, its precise function is still debated. Deletion of the ELG1 gene, encoding a PCNA unloader, can partially suppress the temperature-sensitive pds5-1 allele, but not a complete deletion of PDS5. We carried out a genetic screen for high-copy-number suppressors and another for spontaneously arising mutants, allowing the survival of a pds5Δ elg1Δ strain. Our results show that cells remain viable in the absence of Pds5 provided that there is both an elevation in the level of Mcd1 (which can be due to mutations in the CLN2 gene, encoding a G1 cyclin), and an increase in the level of SUMO-modified PCNA on chromatin (caused by lack of PCNA unloading in elg1Δ mutants). The elevated SUMO-PCNA levels increase the recruitment of the Srs2 helicase, which evicts Rad51 molecules from the moving fork, creating single-stranded DNA (ssDNA) regions that serve as sites for increased cohesin loading and SCC establishment. Thus, our results delineate a double role for Pds5 in protecting the cohesin ring and interacting with the DNA replication machinery.
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