啄木鸟,犀牛/HP1D的同系物,仅在果蝇卵巢中表达,属于异染色质蛋白1家族,犀牛也一样.Rhi通过其N端色域识别富含异染色质标记H3K9me3的piRNA簇,并通过其C端阴影域招募Deadlock,进一步招募Moonshiner,TATA盒结合蛋白相关因子2大亚基的同系物,促进piRNA前体的转录,从而保护基因组。尽管Oxp只拥有色域,它的丢失导致雌性种系中转座子的上调。在这项研究中,我们解决了与组蛋白H3K9me3肽复合物中的Oxp色域的晶体结构。当Oxp色域二聚化时,两个H3K9me3肽以反平行方式与Oxp染色体结构域结合。ITC实验和定点诱变实验表明,E44确定Oxp与H3K9me3的结合能力比Rhi强五倍。此外,我们发现Oxp和Rhi可以形成异二聚体,这可能揭示了在没有CSD的情况下Oxp调节转座子沉默的分子机制。
Oxpecker, the homolog of Rhino/HP1D, exclusively expressed in Drosophila ovaries, belongs to the Heterochromatin Protein 1 family, as does Rhino. Rhi recognizes piRNA clusters enriched with the heterochromatin marker H3K9me3 via its N-terminal
chromodomain and recruits Deadlock via its C-terminal chromoshadow domain, further recruits Moonshiner, a paralog of the TATA box-binding protein-related factor 2 large subunits, to promote transcription of piRNA precursors, thereby protecting the genome. Despite Oxp possessing only the
chromodomain, its loss leads to the upregulation of transposons in the female germline. In this study, we solved the crystal structure of the Oxp
chromodomain in complex with the histone H3K9me3 peptide. As the Oxp
chromodomain dimerizes, two H3K9me3 peptides bind to the Oxp
chromodomain in an antiparallel manner. ITC experiments and site-directed mutagenesis experiments showed that E44 determines Oxp\'s five-fold stronger binding ability to H3K9me3 than that of Rhi. In addition, we found that Oxp and Rhi can form a heterodimer, which may shed light on the molecular mechanism by which Oxp regulates transposon silencing in the absence of CSD.