Pepe Alessandra, West Stephen C
London Research Institute, Cancer Research UK, Clare Hall Laboratories, South Mimms, Herts EN6 3LD, UK.
Nucleic Acids Res. 2014 Apr;42(6):3833-45. doi: 10.1093/nar/gkt1333. Epub 2013 Dec 25.
MUS81 plays important cellular roles in the restart of stalled replication forks, the resolution of recombination intermediates and in telomere length maintenance. Although the actions of MUS81-EME1 have been extensively investigated, MUS81 is the catalytic subunit of two human structure-selective endonucleases, MUS81-EME1 and MUS81-EME2. Little is presently known about the activities of MUS81-EME2. Here, we have purified MUS81-EME2 and compared its activities with MUS81-EME1. We find that MUS81-EME2 is a more active endonuclease than MUS81-EME1 and exhibits broader substrate specificity. Like MUS81-EME1, MUS81-EME2 cleaves 3'-flaps, replication forks and nicked Holliday junctions, and exhibits limited endonuclease activity with intact Holliday junctions. In contrast to MUS81-EME1, however, MUS81-EME2 cuts D-loop recombination intermediates and in so doing disengages the D-loop structure by cleaving the 3'-invading strand. Additionally, MUS81-EME2 acts on 5'-flap structures to cleave off a duplex arm, in reactions that cannot be promoted by MUS81-EME1. These studies suggest that MUS81-EME1 and MUS81-EME2 exhibit similar and yet distinct DNA structure selectivity, indicating that the two MUS81 complexes may promote different nucleolytic cleavage reactions in vivo.
MUS81在停滞复制叉的重新启动、重组中间体的解离以及端粒长度维持中发挥重要的细胞作用。尽管对MUS81-EME1的作用已进行了广泛研究，但MUS81是两种人类结构选择性核酸内切酶MUS81-EME1和MUS81-EME2的催化亚基。目前对MUS81-EME2的活性了解甚少。在此，我们纯化了MUS81-EME2，并将其活性与MUS81-EME1进行了比较。我们发现MUS81-EME2是一种比MUS81-EME1更具活性的核酸内切酶，并且表现出更广泛的底物特异性。与MUS81-EME1一样，MUS81-EME2可切割3'-翼片、复制叉和带切口的霍利迪连接体，并且对完整的霍利迪连接体表现出有限的核酸内切酶活性。然而，与MUS81-EME1不同的是，MUS81-EME2可切割D环重组中间体，并通过切割3'-侵入链来解开D环结构。此外，MUS81-EME2作用于5'-翼片结构以切割掉双链臂，而MUS81-EME1无法促进这些反应。这些研究表明，MUS81-EME1和MUS81-EME2表现出相似但又不同的DNA结构选择性，这表明这两种MUS81复合物可能在体内促进不同的核酸裂解反应。
