Darzacq Xavier, Kittur Nupur, Roy Sujayita, Shav-Tal Yaron, Singer Robert H, Meier U Thomas
Department of Anatomy and Structural Biology, Albert Einstein College of Medicine Bronx, NY 10461, USA.
J Cell Biol. 2006 Apr 24;173(2):207-18. doi: 10.1083/jcb.200601105. Epub 2006 Apr 17.
Mammalian H/ACA RNPs are essential for ribosome biogenesis, premessenger RNA splicing, and telomere maintenance. These RNPs consist of four core proteins and one RNA, but it is not known how they assemble. By interrogating the site of H/ACA RNA transcription, we dissected their biogenesis in single cells and delineated the role of the non-core protein NAF1 in the process. NAF1 and all of the core proteins except GAR1 are recruited to the site of transcription. NAF1 binds one of the core proteins, NAP57, and shuttles between nucleus and cytoplasm. Both proteins are essential for stable H/ACA RNA accumulation. NAF1 and GAR1 bind NAP57 competitively, suggesting a sequential interaction. Our analyses indicate that NAF1 binds NAP57 and escorts it to the nascent H/ACA RNA and that GAR1 then replaces NAF1 to yield mature H/ACA RNPs in Cajal bodies and nucleoli.
哺乳动物的H/ACA核糖核蛋白复合体对于核糖体生物合成、前体信使RNA剪接以及端粒维持至关重要。这些核糖核蛋白复合体由四种核心蛋白和一种RNA组成，但它们的组装方式尚不清楚。通过研究H/ACA RNA的转录位点，我们在单细胞水平剖析了它们的生物发生过程，并阐明了非核心蛋白NAF1在此过程中的作用。NAF1以及除GAR1之外的所有核心蛋白都被招募到转录位点。NAF1与核心蛋白之一NAP57结合，并在细胞核和细胞质之间穿梭。这两种蛋白对于稳定的H/ACA RNA积累都是必不可少的。NAF1和GAR1竞争性地结合NAP57，提示存在顺序性相互作用。我们的分析表明，NAF1结合NAP57并将其护送至新生的H/ACA RNA，然后GAR1取代NAF1，在 Cajal体和核仁中产生成熟的H/ACA核糖核蛋白复合体。
