Abstract
The RNA component of signal recognition particle (SRP) is transcribed by RNA polymerase III, and most steps in SRP biogenesis occur in the nucleolus. Here, we examine processing and quality control of the yeast SRP RNA (scR1). In common with other pol III transcripts, scR1 terminates in a U-tract, and mature scR1 retains a U4–5 sequence at its 3′ end. In cells lacking the exonuclease Rex1, scR1 terminates in a longer U5–6 tail that presumably represents the primary transcript. The 3′ U-tract of scR1 is protected from aberrant processing by the La homologue, Lhp1 and overexpressed Lhp1 apparently competes with both the RNA surveillance system and SRP assembly factors. Unexpectedly, the TRAMP and exosome nuclear RNA surveillance complexes are also implicated in protecting the 3′ end of scR1, which accumulates in the nucleolus of cells lacking the activities of these complexes. Misassembled scR1 has a primary degradation pathway in which Rrp6 acts early, followed by TRAMP-stimulated exonuclease degradation by the exosome. We conclude that the RNA surveillance machinery has key roles in both SRP biogenesis and quality control of the RNA, potentially facilitating the decision between these alternative fates.
Highlights
Stable, non-coding RNAs are required for many key cellular processes, and largely function as components of ribonucleoproteins (RNPs)
We explore the requirements for the TRAMP and exosome complexes for correct localization and degradation of scR1 and, surprisingly, report that both TRAMP and exosome complexes are important to maintain the intact 3 end of scR1
ScR1 levels were greatly reduced in the absence of Srp14, and this was unaltered in cells that lacked either Lhp1 or Rex1
Summary
Non-coding RNAs are required for many key cellular processes, and largely function as components of ribonucleoproteins (RNPs). Rrp is a nuclear-restricted 3 -exonuclease, which functions independently of the exosome. Rrp has both 3 -exonuclease and endonuclease activities, is present throughout the cytoplasm and nucleus as part of the exosome complex and functions in mitochondria [3,4,5,6,7,8,9,10,11]. Mtr is required for several TRAMP-independent activities of the nuclear exosome, including 5.8S rRNA processing and degradation of the 5 external transcribed spacer of pre-rRNA [16,17,18]. The TRAMP and exosome complexes function both in regulated RNA processing during RNP biogenesis, and in RNA surveillance. It remains unclear how the exosome and its cofactors distinguish between RNAs that should undergo precisely regulated processing or be completely degraded
Sign-in/Register to view highlights & summary Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
