Hirota Kouji, Steiner Walter W, Shibata Takehiko, Ohta Kunihiro
Department of Life Sciences, Graduate School of Arts and Sciences, The University of Tokyo, Komaba 3-8-1, Meguroku, Tokyo 153-8902, Japan.
Eukaryot Cell. 2007 Nov;6(11):2072-80. doi: 10.1128/EC.00246-07. Epub 2007 Sep 7.
The ade6-M26 meiotic recombination hot spot of fission yeast is defined by a cyclic AMP-responsive element (CRE)-like heptanucleotide sequence, 5'-ATGACGT-3', which acts as a binding site for the Atf1/Pcr1 heterodimeric transcription factor required for hot spot activation. We previously demonstrated that the local chromatin around the M26 sequence motif alters to exhibit higher sensitivity to micrococcal nuclease before the initiation of meiotic recombination. In this study, we have examined whether or not such alterations in chromatin occur at natural meiotic DNA double-strand break (DSB) sites in Schizosaccharomyces pombe. At one of the most prominent DSB sites, mbs1 (meiotic break site 1), the chromatin structure has a constitutively accessible configuration at or near the DSB sites. The establishment of the open chromatin state and DSB formation are independent of the CRE-binding transcription factor, Atf1. Analysis of the chromatin configuration at CRE-dependent DSB sites revealed both differences from and similarities to mbs1. For example, the tdh1+ locus, which harbors a CRE consensus sequence near the DSB site, shows a meiotically induced open chromatin configuration, similar to ade6-M26. In contrast, the cds1+ locus is similar to mbs1 in that it exhibits a constitutive open configuration. Importantly, Atf1 is required for the open chromatin formation in both tdh1+ and cds1+. These results suggest that CRE-dependent meiotic chromatin changes are intrinsic processes related to DSB formation in fission yeast meiosis. In addition, the results suggest that the chromatin configuration in natural meiotic recombination hot spots can be classified into at least three distinct categories: (i) an Atf1-CRE-independent constitutively open chromatin configuration, (ii) an Atf1-CRE-dependent meiotically induced open chromatin configuration, and (iii) an Atf1-CRE-dependent constitutively open chromatin configuration.
裂殖酵母的ade6-M26减数分裂重组热点由一个环磷酸腺苷反应元件（CRE）样七核苷酸序列5'-ATGACGT-3'定义，该序列作为热点激活所需的Atf1/Pcr1异二聚体转录因子的结合位点。我们先前证明，在减数分裂重组开始之前，M26序列基序周围的局部染色质会发生改变，对微球菌核酸酶表现出更高的敏感性。在本研究中，我们研究了这种染色质改变是否发生在粟酒裂殖酵母的天然减数分裂DNA双链断裂（DSB）位点。在最突出的DSB位点之一mbs1（减数分裂断裂位点1）处，染色质结构在DSB位点或其附近具有组成型可及的构型。开放染色质状态的建立和DSB的形成与CRE结合转录因子Atf1无关。对CRE依赖性DSB位点的染色质构型分析揭示了与mbs1的差异和相似之处。例如，在DSB位点附近含有CRE共有序列的tdh1+基因座显示出减数分裂诱导的开放染色质构型，类似于ade6-M26。相反，cds1+基因座与mbs1相似，因为它表现出组成型开放构型。重要的是，Atf1是tdh1+和cds1+中开放染色质形成所必需的。这些结果表明，CRE依赖性减数分裂染色质变化是与裂殖酵母减数分裂中DSB形成相关的内在过程。此外，结果表明天然减数分裂重组热点中的染色质构型可分为至少三类：（i）Atf1-CRE非依赖性组成型开放染色质构型，（ii）Atf1-CRE依赖性减数分裂诱导的开放染色质构型，以及（iii）Atf1-CRE依赖性组成型开放染色质构型。
