The SPOC domain is a phosphoserine binding module that bridges transcription machinery with co- and post-transcriptional regulators - ChIP-seq

The heptarepeats of the C-terminal domain of Pol II are extensively modified throughout the transcription cycle. The CTD coordinates RNA synthesis and processing by recruiting transcription regulation factors as well as RNA capping, splicing and 3'end processing factors. The SPOC domain of PHF3 was recently identified as a new CTD reader domain specifically binding to phosphorylated Serine-2 residues in adjacent CTD repeats. Here, we establish the SPOC domains of the human proteins DIDO, SHARP and RBM15 as phosphoserine binding modules that can act as CTD readers but also recognize other phosphorylated binding partners. We report the crystal structure of SHARP (SPEN) SPOC-CTD and identify the molecular determinants for its specific binding to phosphorylated Serine-5. PHF3 and DIDO SPOC domains preferentially interact with the Pol II elongation complex, while RBM15 and SHARP SPOC domains engage with the m6A writer and reader proteins. Our findings establish the SPOC domain as a major interface between the transcription machinery and regulators of transcription and co-transcriptional processes. Here we include ChIP seq data from SHARP and PHF3 with and without the SPOC domain.

RNA聚合酶II（Pol II）C端结构域的七联重复序列在整个转录周期中会发生广泛修饰。该C端结构域通过招募转录调控因子以及RNA加帽、剪接与3'端加工因子，协同调控RNA的合成与加工过程。近期研究发现，PHF3蛋白的SPOC结构域（SPOC domain）是一类新型的CTD识别结构域，可特异性结合相邻CTD重复序列中的磷酸化丝氨酸-2残基。本研究证实，人类蛋白DIDO、SHARP及RBM15的SPOC结构域均为磷酸丝氨酸结合模块，不仅可作为CTD识别结构域，还能识别其他磷酸化结合伴侣。我们解析了SHARP（SPEN）SPOC结构域与CTD的晶体结构，并明确了其特异性结合磷酸化丝氨酸-5残基的分子决定因素。PHF3与DIDO的SPOC结构域优先与Pol II延伸复合物相互作用，而RBM15与SHARP的SPOC结构域则可与m6A写入酶及识别蛋白结合。本研究的发现确立了SPOC结构域作为转录机器与转录及共转录过程调控因子之间的关键互作界面。本数据集包含了带有或缺失SPOC结构域时，SHARP与PHF3的染色质免疫沉淀测序（ChIP-seq）数据。