Bystricky Kerstin, Van Attikum Haico, Montiel Maria-Dolores, Dion Vincent, Gehlen Lutz, Gasser Susan M
Laboratoire de Biologie Moléculaire Eucaryote, Bâtiment IBCG, Université de Toulouse, Toulouse, France.
Mol Cell Biol. 2009 Feb;29(3):835-48. doi: 10.1128/MCB.01009-08. Epub 2008 Dec 1.
We have examined the hypothesis that the highly selective recombination of an active mating type locus (MAT) with either HMLalpha or HMRa is facilitated by the spatial positioning of relevant sequences within the budding yeast (Saccharomyces cerevisiae) nucleus. However, both position relative to the nuclear envelope (NE) and the subnuclear mobility of fluorescently tagged MAT, HML, or HMR loci are largely identical in haploid a and alpha cells. Irrespective of mating type, the expressed MAT locus is highly mobile within the nuclear lumen, while silent loci move less and are found preferentially near the NE. The perinuclear positions of HMR and HML are strongly compromised in strains lacking the Silent information regulator, Sir4. However, HMLalpha, unlike HMRa and most telomeres, shows increased NE association in a strain lacking yeast Ku70 (yKu70). Intriguingly, we find that the yKu complex is associated with HML and HMR sequences in a mating-type-specific manner. Its abundance decreases at the HMLalpha donor locus and increases transiently at MATa following DSB induction. Our data suggest that mating-type-specific binding of yKu to HMLalpha creates a local chromatin structure competent for recombination, which cooperates with the recombination enhancer to direct donor choice for gene conversion of the MATa locus.
我们检验了这样一种假说，即活跃的交配型基因座（MAT）与HMLα或HMRa的高度选择性重组是由出芽酵母（酿酒酵母）细胞核内相关序列的空间定位所促进的。然而，在单倍体a型和α型细胞中，相对于核膜（NE）的位置以及荧光标记的MAT、HML或HMR基因座的核内移动性在很大程度上是相同的。无论交配型如何，表达的MAT基因座在核腔内高度移动，而沉默基因座移动较少且优先位于NE附近。在缺乏沉默信息调节因子Sir4的菌株中，HMR和HML的核周位置受到严重影响。然而，与HMRa和大多数端粒不同，HMLα在缺乏酵母Ku70（yKu70）的菌株中显示出与NE的关联增加。有趣的是，我们发现yKu复合体以交配型特异性方式与HML和HMR序列相关联。在DSB诱导后，其丰度在HMLα供体基因座处降低，在MATa处短暂增加。我们的数据表明，yKu与HMLα的交配型特异性结合产生了一种能进行重组的局部染色质结构，它与重组增强子协同作用，指导MATa基因座基因转换的供体选择。
