Sir antagonist 1 (San1) is a ubiquitin ligase
Sir antagonist 1 (San1) is a ubiquitin ligase
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DOI：
10.1074/jbc.m400894200
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发表时间：
2004-06-25
影响因子：
4.8
通讯作者：
Auble, DT
中科院分区：
文献类型：
--
作者：
Dasgupta, A;Ramsey, KL;Auble, DT
爵士拮抗剂1（SAN 1）的突变抑制酿酒酵母中SIR 4和SPT 16的缺陷。San 1含有一个RING结构域，这表明它的功能是通过靶向突变sir 4和spt 16蛋白，通过泛素介导的途径降解。与此一致，突变sir 4和spt 16蛋白在SAN 1细胞中不稳定，但在san 1Delta细胞中稳定。我们证明San 1在体外具有泛素-蛋白质异肽连接酶活性，并且San 1的泛素-蛋白质异肽连接酶活性是其体内功能所必需的。野生型Sir 4的半衰期约为21分钟，san 1 Delta将Sir 4的半衰期延长至>90分钟。相反，san 1 Delta不影响野生型Spt 16、Sir 3、Sir 2或Spt 16相关蛋白Pob 3和Nhp 6的稳定性。SAN 1的缺失也不影响Ste 6 -166的稳定性，Ste 6 -166是酵母中高度不稳定的蛋白质。这些结果支持了San 1控制一类特定的不稳定核蛋白的周转的观点。Sir 4在S.啤酒。Sir 4也可以通过限制Sir 2间接影响rDNA中的沉默。通过删除SAN 1来增加野生型Sir 4的稳定性对沉默只有微妙的影响，这表明酵母中沉默的染色质对Sir 4稳定性的变化有很强的缓冲作用。与San 1作为辅助因子参与调节沉默染色质（包括沉默交配型位点）的想法一致，微阵列分析定义了San 1在几个交配信息素响应基因转录中的小但统计学显著的作用。
Mutations in Sir Antagonist 1 (SAN1) suppress defects in SIR4 and SPT16 in Saccharomyces cerevisiae. San1 contains a RING domain, suggesting that it functions by targeting mutant sir4 and spt16 proteins for degradation by a ubiquitin-mediated pathway. Consistent with this idea, mutant sir4 and spt16 proteins are unstable in SAN1 cells but are stabilized in san1Delta cells. We demonstrate that San1 possesses ubiquitin-protein isopeptide ligase activity in vitro, and the ubiquitin-protein isopeptide ligase activity of San1 is required for its function in vivo. Wild-type Sir4 has a half-life of about 21 min, and san1Delta increased Sir4 half-life to >90 min. In contrast, san1Delta did not affect the stability of wild-type Spt16, Sir3, Sir2, or the Spt16-associated proteins Pob3 and Nhp6. Loss of SAN1 also did not affect the stability of Ste6-166, a highly unstable protein in yeast. These results support the idea that San1 controls the turnover of a specific class of unstable nuclear proteins. Sir4 nucleates the assembly of silent chromatin at telomeres and the silent mating-type loci (HM) in S. cerevisiae. Sir4 can also affect silencing in the rDNA indirectly by sequestering limiting Sir2. Increasing the stability of wild-type Sir4 by deleting SAN1 had only subtle effects on silencing, suggesting that silent chromatin in yeast is robustly buffered against changes in Sir4 stability. Consistent with the idea that San1 participates as an accessory factor to regulate silent chromatin, including the silent mating-type loci, microarray analysis defined a small but statistically significant role for San1 in transcription of several mating pheromone-responsive genes.