Allmang C, Kufel J, Chanfreau G, Mitchell P, Petfalski E, Tollervey D
Institute of Cell and Molecular Biology, University of Edinburgh, Swann Building, King's Buildings, Edinburgh EH9 3JR, UK.
EMBO J. 1999 Oct 1;18(19):5399-410. doi: 10.1093/emboj/18.19.5399.
The yeast nuclear exosome contains multiple 3'-->5' exoribonucleases, raising the question of why so many activities are present in the complex. All components are required during the 3' processing of the 5.8S rRNA, together with the putative RNA helicase Dob1p/Mtr4p. During this processing three distinct steps can be resolved, and hand-over between different exonucleases appears to occur at least twice. 3' processing of snoRNAs (small nucleolar RNAs) that are excised from polycistronic precursors or from mRNA introns is also a multi-step process that involves the exosome, with final trimming specifically dependent on the Rrp6p component. The spliceosomal U4 snRNA (small nuclear RNA) is synthesized from a 3' extended precursor that is cleaved by Rnt1p at sites 135 and 169 nt downstream of the mature 3' end. This cleavage is followed by 3'-->5' processing of the pre-snRNA involving the exosome complex and Dob1p. The exosome, together with Rnt1p, also participates in the 3' processing of the U1 and U5 snRNAs. We conclude that the exosome is involved in the processing of many RNA substrates and that different components can have distinct functions.
酵母核外切体包含多种3'→5'外切核糖核酸酶，这就引发了一个问题：为何该复合体中存在如此多的活性。在5.8S rRNA的3'加工过程中，所有组分连同假定的RNA解旋酶Dob1p/Mtr4p都是必需的。在这个加工过程中，可以分辨出三个不同的步骤，不同外切核酸酶之间的交接似乎至少发生两次。从多顺反子前体或mRNA内含子中切除的小核仁RNA（snoRNA）的3'加工也是一个多步骤过程，涉及外切体，最终的修剪特别依赖于Rrp6p组分。剪接体U4小核RNA（snRNA）由一个3'延伸的前体合成，该前体在成熟3'端下游135和169个核苷酸处被Rnt1p切割。该切割之后是涉及外切体复合体和Dob1p的前体snRNA的3'→5'加工。外切体与Rnt1p一起，也参与U1和U5 snRNA的3'加工。我们得出结论，外切体参与许多RNA底物的加工，并且不同的组分可以具有不同的功能。
