McNees Carolyn J, Conlan Lindus A, Tenis Nora, Heierhorst Jörg
St Vincent's Institute of Medical Research, Fitzroy, Victoria, Australia.
EMBO J. 2005 Jul 6;24(13):2447-57. doi: 10.1038/sj.emboj.7600704. Epub 2005 Jun 2.
Nuclear Rad51 focus formation is required for homology-directed repair of DNA double-strand breaks (DSBs), but its regulation in response to non-DSB lesions is poorly understood. Here we report a novel human SQ/TQ cluster domain-containing protein termed ASCIZ that forms Rad51-containing foci in response to base-modifying DNA methylating agents but not in response to DSB-inducing agents. ASCIZ foci seem to form prior to Rad51 recruitment, and an ASCIZ core domain can concentrate Rad51 in focus-like structures independently of DNA damage. ASCIZ depletion dramatically increases apoptosis after methylating DNA damage and impairs Rad51 focus formation in response to methylating agents but not after ionizing radiation. ASCIZ focus formation and increased apoptosis in ASCIZ-depleted cells depend on the mismatch repair protein MLH1. Interestingly, ASCIZ foci form efficiently during G1 phase, when sister chromatids are unavailable as recombination templates. We propose that ASCIZ acts as a lesion-specific focus scaffold in a Rad51-dependent pathway that resolves cytotoxic repair intermediates, most likely single-stranded DNA gaps, resulting from MLH1-dependent processing of base lesions.
核 Rad51 集落形成是 DNA 双链断裂（DSB）同源定向修复所必需的，但对其响应非 DSB 损伤的调控了解甚少。在此，我们报告了一种新型的含人 SQ/TQ 簇结构域的蛋白质，称为 ASCIZ，它在响应碱基修饰的 DNA 甲基化剂时形成含 Rad51 的集落，但在响应 DSB 诱导剂时不形成。ASCIZ 集落似乎在 Rad51 募集之前形成，并且 ASCIZ 核心结构域可以独立于 DNA 损伤将 Rad51 集中在类似集落的结构中。ASCIZ 缺失显著增加甲基化 DNA 损伤后的细胞凋亡，并损害对甲基化剂的 Rad51 集落形成，但在电离辐射后不会。ASCIZ 集落形成以及 ASCIZ 缺失细胞中细胞凋亡增加取决于错配修复蛋白 MLH1。有趣的是，当姐妹染色单体不可用作重组模板时，ASCIZ 集落在 G1 期有效形成。我们提出 ASCIZ 在 Rad51 依赖的途径中作为损伤特异性集落支架发挥作用，该途径解决由 MLH1 依赖的碱基损伤处理产生的细胞毒性修复中间体，最有可能是单链 DNA 间隙。
