Institute of Molecular Biology, University of Oregon, Eugene, OR 97403, USA.
Proc Natl Acad Sci U S A. 2012 Apr 10;109(15):5651-6. doi: 10.1073/pnas.1200318109. Epub 2012 Mar 26.
The half-a-tetratricopeptide repeat (HAT) motif is a helical repeat motif found in proteins that influence various aspects of RNA metabolism, including rRNA biogenesis, RNA splicing, and polyadenylation. This functional association with RNA suggested that HAT repeat tracts might bind RNA. However, RNA binding activity has not been reported for any HAT repeat tract, and recent literature has emphasized a protein binding role. In this study, we show that a chloroplast-localized HAT protein, HCF107, is a sequence-specific RNA binding protein. HCF107 consists of 11 tandem HAT repeats and short flanking regions that are also predicted to form helical hairpins. The minimal HCF107 binding site spans ∼11 nt, consistent with the possibility that HAT repeats bind RNA through a modular one repeat-1 nt mechanism. Binding of HCF107 to its native RNA ligand in the psbH 5' UTR remodels local RNA structure and protects the adjacent RNA from exonucleases in vitro. These activities can account for the RNA stabilizing, RNA processing, and translational activation functions attributed to HCF107 based on genetic data. We suggest that analogous activities contribute to the functions of HAT domains found in ribonucleoprotein complexes in the nuclear-cytosolic compartment.
半四肽重复（HAT）基序是一种存在于蛋白质中的螺旋重复基序，它影响 RNA 代谢的各个方面，包括 rRNA 生物发生、RNA 剪接和多聚腺苷酸化。这种与 RNA 的功能关联表明 HAT 重复序列可能与 RNA 结合。然而，尚未报道任何 HAT 重复序列具有 RNA 结合活性，最近的文献强调了其作为蛋白质结合的作用。在本研究中，我们表明定位于叶绿体的 HAT 蛋白 HCF107 是一种序列特异性的 RNA 结合蛋白。HCF107 由 11 个串联的 HAT 重复序列和短的侧翼区域组成，这些侧翼区域也被预测形成螺旋发夹。HCF107 的最小结合位点跨越约 11 个核苷酸，这表明 HAT 重复序列可能通过模块化的一个重复-1 个核苷酸机制与 RNA 结合。HCF107 与其天然 RNA 配体在 psbH 5'UTR 上的结合重塑了局部 RNA 结构，并在体外保护相邻的 RNA 免受核酸外切酶的作用。这些活性可以解释基于遗传数据归因于 HCF107 的 RNA 稳定、RNA 加工和翻译激活功能。我们认为，类似的活性有助于核质细胞中核蛋白复合物中 HAT 结构域的功能。
