Misregulation of 2μm circle copy number in a SUMO pathway mutant
Misregulation of 2μm circle copy number in a SUMO pathway mutant
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DOI：
10.1128/mcb.25.10.4311-4320.2005
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发表时间：
2005-05-01
影响因子：
5.3
通讯作者：
Johnson, ES
中科院分区：
文献类型：
--
作者：
Chen, XL;Reindle, A;Johnson, ES
类泛素蛋白SUMO与其他蛋白质的连接在酿酒酵母中是一个重要过程。然而，缺乏SUMO连接酶Siz1和Siz2/Nfi1的酵母突变体是可存活的，尽管它们的SUMO偶联水平显著降低。这种siz1∆siz2∆双突变体对低温敏感，并且具有一种不寻常的表型，即它形成形状不规则的菌落，其中包含外观正常的野生型细胞区域以及在G₂/M期停滞的增大细胞区域。我们发现这些表型是由于内源性酵母质粒——2μm环状质粒的拷贝数调控失常所致。siz1∆siz2∆突变体的2μm质粒水平比野生型菌株高多达40倍。此外，2μm质粒是导致siz1∆siz2∆突变体明显生长缺陷的原因，因为缺乏2μm质粒的siz1∆siz2∆[cir(0)]菌株不再具有异质性，并且表现出与野生型相似的生长特征。SUMO对2μm质粒产生影响的可能机制由以下发现所提示：2μm质粒编码的四种蛋白质中的两种，即Flp1重组酶和Rep2，都被SUMO共价修饰。我们的数据表明SUMO连接对Flp1水平起负调控作用，这可能部分解释了siz1∆siz2∆菌株中2μm质粒拷贝数增加的原因。
Attachment of the ubiquitin-like protein SUMO to other proteins is an essential process in Saccharomyces cerevisiae. However, yeast mutants lacking the SUMO ligases Siz1 and Siz2/Nfi1 are viable, even though they show dramatically reduced levels of SUMO conjugation. This siz1 Delta siz2 Delta double mutant is cold sensitive and has an unusual phenotype in that it forms irregularly shaped colonies that contain sectors of wild-type-appearing cells as well as sectors of enlarged cells that are arrested in G(2)/M. We have found that these phenotypes result from misregulation of the copy number of the endogenous yeast plasmid, the 2 mu m circle. siz1 Delta siz2 Delta mutants have up to 40-fold-higher levels of 2 mu m than do wild-type strains. Furthermore, 2 mu m is responsible for the siz1 Delta siz2 Delta mutant's obvious growth defects, as siz1 Delta siz2 Delta [cir(0)] strains, which lack 2 mu m, are no longer heterogeneous and show growth characteristics similar to those of the wild type. Possible mechanisms for SUMO's effect on 2 mu m are suggested by the finding that both Flp1 recombinase and Rep2, two of the four proteins encoded by 2 mu m, are covalently modified by SUMO. Our data suggest that SUMO attachment negatively regulates Flp1 levels, which may partially account for the increased 2 mu m copy number in the siz1 Delta siz2 Delta strain.