Cohesin acetylation speeds the replication fork

摘要

Cohesin not only links sister chromatids but also inhibits the transcriptional machinery's interaction with and movement along chromatin. In contrast, replication forks must traverse such cohesin-associated obstructions to duplicate the entire genome in S phase. How this occurs is unknown. Through single-molecule analysis, we demonstrate that the replication factor C (RFC)-CTF18 clamp loader (RFC~(CTF18)) controls the velocity, spacing and restart activity of replication forks in human cells and is required for robust acetylation of cohesin's SMC3 subunit and sister chromatid cohesion. Unexpectedly, we discovered that cohesin acetylation itself is a central determinant of fork proces-sivity, as slow-moving replication forks were found in cells lacking the Ecol-related acetyltransferases ESCO1 or ESCO2 (refs 8-10) (including those derived from Roberts' syndrome patients, in whom ESCO2 is biallelically mutated11) and in cells expressing a form of SMC3 that cannot be acetylated. This defect was a consequence of cohesin's hyperstable interaction with two regulatory cofactors, WAPL and PDS5A (refs 12,13); removal of either cofac-tor allowed forks to progress rapidly without ESCOl, ESCO2, or RFC~(CTF18). Our results show a novel mechanism for clamp-loader-dependent fork progression, mediated by the post-translational modification and structural remodelling of the cohesin ring. Loss of this regulatory mechanism leads to the spontaneous accrual of DNA damage and may contribute to the abnormalities of the Roberts' syndrome cohesinopathy.%整合素环在细胞分裂过程中围绕着姐妹DNA分rn子对，使它们能够正确分开。这些环抑制转录rn细胞器的进程，但并不阻止复制细胞器在细rn胞周期的S一阶段复制基因组。现在，单分子rn分析表明，一个复制复合物(被称为复制因子rnC-CTF18 clamp loader)使整合素乙酰化，从rn而减低整合素与调控因子的关联，推动复制叉rn的进程。乙酰化的失去(如在罗伯茨综合征患rn者的细胞中所观察到的那样)，会造成叉进程rn的缺陷及DNA损伤的积累。