Lsm proteins and RNA processing. Biochem Soc Trans

Wellcome Trust Centre for Cell Biology, School of Biological Sciences, University of Edinburgh, King's Buildings, Mayfield Road, Edinburgh EH9 3JR, U.K.
Biochemical Society Transactions (Impact Factor: 3.19). 07/2005; 33(Pt 3):433-8. DOI: 10.1042/BST0330433
Source: PubMed


Sm and Lsm proteins are ubiquitous in eukaryotes and form complexes that interact with RNAs involved in almost every cellular process. My laboratory has studied the Lsm proteins in the yeast Saccharomyces cerevisiae, identifying in the nucleus and cytoplasm distinct complexes that affect pre-mRNA splicing and degradation, small nucleolar RNA, tRNA processing, rRNA processing and mRNA degradation. These activities suggest RNA chaperone-like roles for Lsm proteins, affecting RNA-RNA and/or RNA-protein interactions. This article reviews the properties of the Sm and Lsm proteins and structurally and functionally related proteins in archaea and eubacteria.

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Available from: Jean D Beggs
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    • "Sm-like proteins (LSms) are a highly conserved family of proteins in eukaryotes both in terms of sequence and functions. LSms typically exist as heptameric complexes and play roles in multiple aspects of RNA metabolism [7-9]. The heptameric LSm1-7 cytoplasmic complex is located in discrete cytoplasmic structures called P-bodies, which are conserved in all eukaryotes and are thought to be involved in decapping and 5′ to 3′ RNA degradation [10,11]. "
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    ABSTRACT: Sm-like proteins are highly conserved proteins that form the core of the U6 ribonucleoprotein and function in several mRNA metabolism processes, including pre-mRNA splicing. Despite their wide occurrence in all eukaryotes, little is known about the roles of Sm-like proteins in the regulation of splicing. Here, through comprehensive transcriptome analyses, we demonstrate that depletion of the Arabidopsis supersensitive to abscisic acid and drought 1 gene (SAD1), which encodes Sm-like protein 5 (LSm5), promotes an inaccurate selection of splice sites that leads to a genome-wide increase in alternative splicing. In contrast, overexpression of SAD1 strengthens the precision of splice-site recognition and globally inhibits alternative splicing. Further, SAD1 modulates the splicing of stress-responsive genes, particularly under salt-stress conditions. Finally, we find that overexpression of SAD1 in Arabidopsis improves salt tolerance in transgenic plants, which correlates with an increase in splicing accuracy and efficiency for stress-responsive genes. We conclude that SAD1 dynamically controls splicing efficiency and splice-site recognition in Arabidopsis, and propose that this may contribute to SAD1-mediated stress tolerance through the metabolism of transcripts expressed from stress-responsive genes. Our study not only provides novel insights into the function of Sm-like proteins in splicing, but also uncovers new means to improve splicing efficiency and to enhance stress tolerance in a higher eukaryote.
    Full-text · Article · Jan 2014 · Genome biology
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    • "Both studies concluded that uridylation favours the 5′ to 3′ directionality of RNA decay and supports the idea that uridylation could stabilize 3′-ends (17,18). In fact, U-tracts that terminate the transcription of RNA polymerase III precursors are well known to prevent 3′ to 5′ degradation by promoting the binding of the La protein and the Lsm2-8 heptameric complex in the nucleus (43). Interestingly, a link between uridylation and binding of the cytosolic Lsm1-7 complex also exists. "
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    ABSTRACT: Degradation of mRNAs is usually initiated by deadenylation, the shortening of long poly(A) tails to oligo(A) tails of 12–15 As. Deadenylation leads to decapping and to subsequent 5′ to 3′ degradation by XRN proteins, or alternatively 3′ to 5′ degradation by the exosome. Decapping can also be induced by uridylation as shown for the non-polyadenylated histone mRNAs in humans and for several mRNAs in Schizosaccharomyces pombe and Aspergillus nidulans. Here we report a novel role for uridylation in preventing 3′ trimming of oligoadenylated mRNAs in Arabidopsis. We show that oligo(A)-tailed mRNAs are uridylated by the cytosolic UTP:RNA uridylyltransferase URT1 and that URT1 has no major impact on mRNA degradation rates. However, in absence of uridylation, oligo(A) tails are trimmed, indicating that uridylation protects oligoadenylated mRNAs from 3′ ribonucleolytic attacks. This conclusion is further supported by an increase in 3′ truncated transcripts detected in urt1 mutants. We propose that preventing 3′ trimming of oligo(A)-tailed mRNAs by uridylation participates in establishing the 5′ to 3′ directionality of mRNA degradation. Importantly, uridylation prevents 3′ shortening of mRNAs associated with polysomes, suggesting that a key biological function of uridylation is to confer 5′ to 3′ polarity in case of co-translational mRNA decay.
    Full-text · Article · Jun 2013 · Nucleic Acids Research
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    • "Distinctive and conserved features of many snRNAs are both the presence of a 5′-2,2,7mG-cap (Tri-Methyl-Guanosine-cap (TMG-cap) and an Sm binding site. This site provides a platform for the assembly of the heteroheptameric Sm complex, comprised of Sm protein products of SMB1, SMD1, SMD2, SMD3, SME1, SMX2 and SMX3 genes [11]. Intriguingly, another cellular non-coding RNA (ncRNA), telomerase RNA, also harbors these elements. "
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    ABSTRACT: A key question in the field of RNA regulation is how some exosome substrates, such as spliceosomal snRNAs and telomerase RNA, evade degradation and are processed into stable, functional RNA molecules. Typical feature of these non-coding RNAs is presence of the Sm complex at the 3'end of the mature RNA molecule. Here, we report that in Saccharomyces cerevisiae presence of intact Sm binding site is required for the exosome-mediated processing of telomerase RNA from a polyadenylated precursor into its mature form and is essential for its function in elongating telomeres. Additionally, we demonstrate that the same pathway is involved in the maturation of snRNAs. Furthermore, the insertion of an Sm binding site into an unstable RNA that is normally completely destroyed by the exosome, leads to its partial stabilization. We also show that telomerase RNA accumulates in Schizosaccharomyces pombe exosome mutants, suggesting a conserved role for the exosome in processing and degradation of telomerase RNA. In summary, our data provide important mechanistic insight into the regulation of exosome dependent RNA processing as well as telomerase RNA biogenesis.
    Full-text · Article · Jun 2013 · PLoS ONE
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