Rockefeller University, New York, NY 10065, USA.
Mol Cell. 2009 Dec 11;36(5):768-81. doi: 10.1016/j.molcel.2009.11.011.
Ribosomal processing requires a series of endo- and exonucleolytic steps for the production of mature ribosomes, of which most have been described. To ensure ribosome synthesis, 3' end formation of rRNA uses multiple nucleases acting in parallel; however, a similar parallel mechanism had not been described for 5' end maturation. Here, we identify Rrp17p as a previously unidentified 5'-3' exonuclease essential for ribosome biogenesis, functioning with Rat1p in a parallel processing pathway analogous to that of 3' end formation. Rrp17p is required for efficient exonuclease digestion of the mature 5' ends of 5.8S(S) and 25S rRNAs, contains a catalytic domain close to its N terminus, and is highly conserved among higher eukaryotes, being a member of a family of exonucleases. We show that Rrp17p binds late pre-60S ribosomes, accompanying them from the nucleolus to the nuclear periphery, and provide evidence for physical and functional links between late 60S subunit processing and export.
核糖体加工需要一系列内切和外切核酸酶步骤，以产生成熟的核糖体，其中大多数步骤已经被描述。为了确保核糖体的合成，rRNA 的 3'端形成使用了多种同时作用的核酸酶；然而，对于 5'端成熟，尚未描述类似的平行机制。在这里，我们确定 Rrp17p 是一种以前未被识别的 5'-3'外切核酸酶，对于核糖体生物发生是必不可少的，与 Rat1p 一起在类似于 3'端形成的平行加工途径中发挥作用。Rrp17p 对于成熟的 5.8S(S) 和 25S rRNAs 的 5'端的有效外切酶消化是必需的，它在 N 端附近含有一个催化结构域，并且在高等真核生物中高度保守，是一类外切核酸酶的成员。我们表明 Rrp17p 结合晚期前 60S 核糖体，伴随它们从核仁到核周，并提供了晚期 60S 亚基加工和输出之间的物理和功能联系的证据。
