超越SAM：多梳-group蛋白polyhomeotic的作用机制

摘要(中文译文)

多梳组（PcG）系统调控不同物种的发育转变和细胞状态。两个主要的PcG复合物，即多梳抑制复合物1和2（PRC1、PRC2），调控转录并通过染色质形成表观遗传记忆。Polyhomeotic（Ph）是一个重要的PRC1亚基，但受到的关注相对较少，这可能是因为它既不参与组蛋白翻译后修饰（PTM）的沉积也不参与其识别。相反，Ph通过其标志性的聚合性不育α基序（SAM）调控染色质架构。本文综述了Ph及哺乳动物polyhomeotic样蛋白（PHC）的生物化学与功能。我们描述了SAM聚合的作用以及不依赖聚合的SAM必要功能的证据。本文还探讨了Ph的进化起源，以及无序区和有序区可能协同进化以维持但改变Ph功能的可能性。最后，我们将动物中SAM的功能与植物PcG蛋白中新发现的聚合活性进行了类比，后者可能反映了趋同进化。

Abstract

The Polycomb Group (PcG) system controls developmental transitions and cell states across species. Two main PcG complexes, Polycomb Repressive Complexes 1 and 2 (PRC1, PRC2), regulate transcription and form epigenetic memory through chromatin. Polyhomeotic (Ph) is an essential PRC1 subunit that has received relatively little attention, perhaps because it is not implicated in either depositing or recognizing histone post-translational modifications (PTMs). Instead, Ph regulates chromatin architecture through its hallmark polymerizing sterile alpha motif (SAM). Here we review the biochemistry and function of Ph and mammalian polyhomeotic-like proteins (PHCs). We describe the role of SAM polymerization and evidence for essential polymerization-independent SAM functions. The evolutionary origins of Ph and possible co-evolution of disordered and ordered regions to maintain but modify Ph function are considered. Finally, we draw parallels between SAM function in animals and a recently discovered polymerization activity in a plant PcG protein that may reflect convergent evolution.

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