Callahan Kevin P, Butler J Scott
Department of Biochemistry and Biophysics, University of Rochester Medical Center, Rochester, NY 14642, USA.
Nucleic Acids Res. 2008 Dec;36(21):6645-55. doi: 10.1093/nar/gkn743. Epub 2008 Oct 21.
The RNA exosome processes and degrades RNAs in archaeal and eukaryotic cells. Exosomes from yeast and humans contain two active exoribonuclease components, Rrp6p and Dis3p/Rrp44p. Rrp6p is concentrated in the nucleus and the dependence of its function on the nine-subunit core exosome and Dis3p remains unclear. We found that cells lacking Rrp6p accumulate poly(A)+ rRNA degradation intermediates distinct from those found in cells depleted of Dis3p, or the core exosome component Rrp43p. Depletion of Dis3p in the absence of Rrp6p causes a synergistic increase in the levels of degradation substrates common to the core exosome and Rrp6p, but has no effect on Rrp6p-specific substrates. Rrp6p lacking a portion of its C-terminal domain no longer co-purifies with the core exosome, but continues to carry out RNA 3'-end processing of 5.8S rRNA and snoRNAs, as well as the degradation of certain truncated Rrp6-specific rRNA intermediates. However, disruption of Rrp6p-core exosome interaction results in the inability of the cell to efficiently degrade certain poly(A)+ rRNA processing products that require the combined activities of Dis3p and Rrp6p. These findings indicate that Rrp6p may carry out some of its critical functions without physical association with the core exosome.
RNA外切体在古细菌和真核细胞中加工和降解RNA。酵母和人类的外切体含有两种活性核糖核酸外切酶成分，即Rrp6p和Dis3p/Rrp44p。Rrp6p集中在细胞核中，其功能对九亚基核心外切体和Dis3p的依赖性尚不清楚。我们发现，缺乏Rrp6p的细胞会积累多聚腺苷酸（poly(A)+）rRNA降解中间体，这些中间体与缺乏Dis3p或核心外切体成分Rrp43p的细胞中发现的中间体不同。在缺乏Rrp6p的情况下耗尽Dis3p会导致核心外切体和Rrp6p共有的降解底物水平协同增加，但对Rrp6p特异性底物没有影响。缺失部分C末端结构域的Rrp6p不再与核心外切体共纯化，但继续进行5.8S rRNA和小核仁RNA（snoRNAs） 的RNA 3'末端加工，以及某些截短的RrpEx6特异性rRNA中间体的降解。然而，Rrp6p-核心外切体相互作用的破坏导致细胞无法有效降解某些需要Dis3p和Rrp6p联合活性的多聚腺苷酸（poly(A)+）rRNA加工产物。这些发现表明，Rrp6p可能在不与核心外切体物理结合的情况下执行其一些关键功能。
