Nucleic acid-binding proteins of the Sac10b family, also known as Alba, are widely distributed in Archaea. However, the physiological roles of these proteins have yet to be clarified. Here, we show that Sis10b, a member of the Sac10b family from the hyperthermophilic archaeon Sulfolobus islandicus, was active in RNA strand exchange, duplex RNA unwinding in vitro and RNA unfolding in a heterologous host cell. This protein exhibited temperature-dependent binding preference for ssRNA over dsRNA and was more efficient in RNA unwinding and RNA unfolding at elevated temperatures. Notably, alanine substitution of a highly conserved basic residue (K) at position 17 in Sis10b drastically reduced the ability of this protein to catalyse RNA strand exchange and RNA unwinding. Additionally, the preferential binding of Sis10b to ssRNA also depended on the presence of K17 or R17. Furthermore, normal growth was restored to a slow-growing Sis10b knockdown mutant by overproducing wild-type Sis10b but not by overproducing K17A in this mutant strain. Our results indicate that Sis10b is an RNA chaperone that likely functions most efficiently at temperatures optimal for the growth of S. islandicus, and K17 is essential for the chaperone activity of the protein.

中文翻译：

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来自Sulfolobus islandicus的Sac10b同源物是一种RNA伴侣。

Sac10b家族的核酸结合蛋白（也称为Alba）广泛分布在古细菌中。但是，这些蛋白质的生理作用尚未阐明。在这里，我们显示Sis10b，来自超嗜热古细菌Sulfolobus islandicus的Sac10b家族的成员，在RNA链交换，双链体RNA体外解离中具有活性RNA在异源宿主细胞中展开。与dsRNA相比，该蛋白对ssRNA表现出温度依赖性的结合偏好，并且在升高的温度下，RNA解链和RNA折叠更有效。值得注意的是，Sis10b中17位高度保守的碱性残基（K）的丙氨酸取代极大地降低了该蛋白质催化RNA链交换和RNA解链的能力。另外，Sis10b与ssRNA的优先结合也取决于K17或R17的存在。此外，通过在该突变株中过量生产野生型Sis10b，而不是通过过量生产K17A，可以恢复生长缓慢的Sis10b敲低突变体的正常生长。我们的结果表明，Sis10b是一种RNA分子伴侣，它可能在最适合小岛链球菌生长的温度下发挥最有效的作用。，而K17对于该蛋白的伴侣活性至关重要。