Akhmedov A T, Frei C, Tsai-Pflugfelder M, Kemper B, Gasser S M, Jessberger R
Basel Institute for Immunology, Grenzacherstrasse 487, CH-4005 Basel, Switzerland.
J Biol Chem. 1998 Sep 11;273(37):24088-94. doi: 10.1074/jbc.273.37.24088.
Structural maintenance of chromosomes (SMC) proteins interact with DNA in chromosome condensation, sister chromatid cohesion, DNA recombination, and gene dosage compensation. How individual SMC proteins and their functional domains bind DNA has not been described. We demonstrate the ability of the C-terminal domains of Saccharomyces cerevisiae SMC1 and SMC2 proteins, representing two major subfamilies with different functions, to bind DNA in an ATP-independent manner. Three levels of DNA binding specificity were observed: 1) a >100-fold preference for double-stranded versus single-stranded DNA; 2) a high affinity for DNA fragments able to form secondary structures and for synthetic cruciform DNA molecules; and 3) a strong preference for AT-rich DNA fragments of particular types. These include fragments from the scaffold-associated regions, and an alternating poly(dA-dT)-poly(dT-dA) synthetic polymer, as opposed to a variety of other polymers. Reannealing of complementary DNA strands is also promoted primarily by the C-terminal domains. Consistent with their in vitro DNA binding activity, we show that overexpression of the SMC C termini increases plasmid loss without altering viability or cell cycle progression.
染色体结构维持（SMC）蛋白在染色体浓缩、姐妹染色单体黏连、DNA重组和基因剂量补偿过程中与DNA相互作用。单个SMC蛋白及其功能结构域如何结合DNA尚未见报道。我们证明了酿酒酵母SMC1和SMC2蛋白的C末端结构域（分别代表两个具有不同功能的主要亚家族）以不依赖ATP的方式结合DNA的能力。观察到了三个层次的DNA结合特异性：1）对双链DNA比对单链DNA有>100倍的偏好；2）对能够形成二级结构的DNA片段和合成十字形DNA分子具有高亲和力；3）对特定类型的富含AT的DNA片段有强烈偏好。这些片段包括来自支架相关区域的片段，以及交替的聚（dA-dT）-聚（dT-dA）合成聚合物，而不是各种其他聚合物。互补DNA链的复性也主要由C末端结构域促进。与它们在体外的DNA结合活性一致，我们表明SMC C末端的过表达增加了质粒丢失率，而不改变活力或细胞周期进程。
