Department of Biochemistry and Molecular Biology, University of Maryland School of Medicine, Baltimore, Maryland 21201, United States.
Biochemistry. 2010 Dec 14;49(49):10357-70. doi: 10.1021/bi101518x. Epub 2010 Nov 19.
Mtr4p is a DEVH-box helicase required for 3'-end processing and degradation of various nuclear RNA substrates. In particular, Mtr4p is essential for the creation of 5.8S rRNA, U4 snRNA, and some snoRNAs and for the degradation of cryptic unstable transcripts (CUTs), aberrant mRNAs, and aberrant tRNAs. Many instances of 3'-end processing require limited polyadenylation to proceed. While polyadenylation can signal degradation in species from bacteria to humans, the mechanism whereby polyadenylated substrates are delivered to the degradation machinery is unknown. Our previous work has shown that Mtr4p preferentially binds poly(A) RNA. We suspect that this preference aids in targeting polyadenylated RNAs to the exosome. In these studies, we have investigated the mechanism underlying the preference of Mtr4p for poly(A) substrates as a means of understanding how Mtr4p might facilitate targeting. Our analysis has revealed that recognition of poly(A) substrates involves sequence-specific changes in the architecture of Mtr4p-RNA complexes. Furthermore, these differences significantly affect downstream activities. In particular, homopolymeric stretches like poly(A) ineffectively stimulate the ATPase activity of Mtr4p and suppress the rate of dissociation of the Mtr4p-RNA complex. These findings indicate that the Mtr4p-poly(A) complex is unique and ideally suited for targeting key substrates to the exosome.
Mtr4p 是一种 DEVH-box 解旋酶，需要对各种核 RNA 底物进行 3'-末端加工和降解。特别是，Mtr4p 对于 5.8S rRNA、U4 snRNA 和一些 snoRNA 的产生以及隐源性不稳定转录物（CUTs）、异常 mRNA 和异常 tRNA 的降解是必不可少的。许多 3'-末端加工实例需要进行有限的聚腺苷酸化才能进行。虽然聚腺苷酸化可以在从细菌到人类的物种中发出降解信号，但聚腺苷酸化底物被递送到降解机制的机制尚不清楚。我们之前的工作表明，Mtr4p 优先结合 poly(A) RNA。我们推测这种偏好有助于将多聚腺苷酸化的 RNA 靶向到外切体。在这些研究中，我们研究了 Mtr4p 对 poly(A) 底物偏好的机制，以了解 Mtr4p 如何促进靶向。我们的分析表明，poly(A) 底物的识别涉及 Mtr4p-RNA 复合物结构的序列特异性变化。此外，这些差异会显著影响下游活动。特别是，像 poly(A) 这样的同聚体延伸会无效地刺激 Mtr4p 的 ATPase 活性，并抑制 Mtr4p-RNA 复合物的解离速率。这些发现表明，Mtr4p-poly(A) 复合物是独特的，非常适合将关键底物靶向外切体。
