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. 2012 Nov 9;48(3):422-33.
doi: 10.1016/j.molcel.2012.08.013. Epub 2012 Sep 20.

Transcriptome-wide analysis of exosome targets

Claudia Schneider  1 , Grzegorz Kudla, Wiebke Wlotzka, Alex Tuck, David Tollervey
Affiliations

Transcriptome-wide analysis of exosome targets

Claudia Schneider et al. Mol Cell. .

Abstract

The exosome plays major roles in RNA processing and surveillance but the in vivo target range and substrate acquisition mechanisms remain unclear. Here we apply in vivo RNA crosslinking (CRAC) to the nucleases (Rrp44, Rrp6), two structural subunits (Rrp41, Csl4) and a cofactor (Trf4) of the yeast exosome. Analysis of wild-type Rrp44 and catalytic mutants showed that both the CUT and SUT classes of non-coding RNA, snoRNAs and, most prominently, pre-tRNAs and other Pol III transcripts are targeted for oligoadenylation and exosome degradation. Unspliced pre-mRNAs were also identified as targets for Rrp44 and Rrp6. CRAC performed using cleavable proteins (split-CRAC) revealed that Rrp44 endonuclease and exonuclease activities cooperate on most substrates. Mapping oligoadenylated reads suggests that the endonuclease activity may release stalled exosome substrates. Rrp6 was preferentially associated with structured targets, which frequently did not associate with the core exosome indicating that substrates follow multiple pathways to the nucleases.

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Figures

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Graphical abstract
Figure 1
Figure 1
Comparison of Targets of Wild-Type and Mutant Rrp44 (A) Domain structure of S. cerevisiae Rrp44, including a C-terminal His-TEV protease-protein A (HTP) tag for purification. Point mutations inactivating the endonuclease (rrp44-endo) or exonuclease (rrp44-exo) activity of Rrp44 are indicated. (B) Outline of the CRAC crosslinking technique. (C–E) Illumina high-throughput sequencing of cDNA libraries generated from crosslinked RNAs recovered with purified wild-type Rrp44 and the Rrp44-endo and Rrp44-exo mutants, as well as the exosome cofactor Trf4. Here, and in all other illustrations, sequencing data of individual biological replicate experiments was mapped to the yeast genome using Novoalign and normalized to hits per million mapped sequences (hpm). (C) Heat maps for main substrate groups. Numbers of reads mapped to individual RNAs are shown in shades of red. (D) Frequencies of non-templated terminal oligo(A) sequence reads in data sets for wild-type Rrp44 and catalytic mutants, and the exosome cofactor Trf4. Data sets are filtered either for total reads, or for Pol I, Pol II and Pol III transcripts, that contain 2 or more non-templated As. (E) Transcriptome-wide binding profiles. Bar diagrams illustrate the percentage of all sequences mapped to the functional RNA classes indicated on the right of the figure.
Figure 2
Figure 2
The Exosome and Cofactors Target RNA Pol III Transcripts (A) Proportion of reads mapped to products of RNA Polymerases I, II and III recovered with wild-type Rrp44 and catalytic mutants, and with the exosome cofactor Trf4. (B) Northern analyses showing pre-tRNA and other Pol III RNA accumulation in strains expressing Rrp44 mutants. A GAL::rrp44 strain was transformed with plasmids expressing either wild-type or mutant Rrp44 protein, or an empty vector pRS315. The mutants analyzed are Rrp44-exo, Rrp44-endo and Rrp44-endo-exo (see Figure 1A). RNA was isolated from strains grown at 30°C under permissive conditions (0) and 10 hr after transcriptional repression (10). RNA was separated on an 8% polyacrylamide/ 8M urea gel and either detected by northern hybridization with oligonucleotide probes (Table S1) or by staining with EtBr. A schematic representation of the identified species is shown.
Figure 3
Figure 3
Split-CRAC Allows the Targets of the N-Terminal and C-Terminal Regions of Rrp44 To Be Distinguished (A) Cleavable Rrp44-expression constructs used for split-CRAC. The location of the PreScission protease (PP) cleavage site, which allows the separation of N- and C-terminal domains (NTD and CTD) in vitro, and the purification tags are indicated. (B) Outline of the split-CRAC crosslinking technique. (C) Distribution of reads recovered with full-length and cleaved wild-type Rrp44 (left) and the Rrp44-exo mutant (right). Sequencing data were analyzed as in Figure 1.
Figure 4
Figure 4
Comparison of Rrp44 Domains in Split-CRAC (A) Secondary structure of U6 snRNA (112 nt) from S. cerevisiae. Major sites of microdeletions are circled. These are due to reverse transcriptase stops at the crosslinked nucleotide. Prominent sites of oligoadenylation are indicated in green and are located 3′ to the major crosslinking sites. The positions of the first non-templated adenosines in A-tailed reads are indicated in green. (B) Predicted secondary structure for the pre-rRNA 5′-ETS region (699 nt) from S. cerevisiae. Processing sites A0 and A1 are indicated by arrowheads. (C) Read coverage for full-length and cleaved Rrp44 (red) and Rrp44-exo (black) in the U6 snRNA (left) and the pre-rRNA 5′-ETS region (right). Mapped reads (hits) are depicted in red (Rrp44) or gray (Rrp44-exo); positions of microdeletions (dels) are indicated in black. Data sets used for analysis were either unfiltered (Total) or filtered for reads containing 2 or more non-templated As (A-tailed). FL – full-length protein; N – NTD; C – CTD. (D) Proposed model for the cooperative action of the endonuclease and exonuclease activities of Rrp44 and the TRAMP complex on structured RNA substrates. Many substrates are threaded through the exosome barrel to reach the active sites of Rrp44, which interacts with the exosome core via the NTD (Bonneau et al., 2009; Malet et al., 2010; Schaeffer et al., 2009; Schneider et al., 2009). Proteins of the RNase II family, which includes the exonuclease domain of Rrp44, are strongly processive and bind substrates tightly in the active site cleft (Zuo et al., 2006). This presumably allows Rrp44 to actively pull substrate RNAs in through the complex (1). However, only single stranded RNAs can enter the lumen of the exosome, so stable RNA-RNA or RNA-protein structures in the substrate potentially lead to stalled complexes, in which the 3′ end is tightly but non-productively bound by Rrp44 (2). We postulate that under these circumstances, the PIN domain cleaves the RNA (3), allowing substrate release (4). The substrate could then be re-adenylated by the TRAMP complex (5) and reloaded into the exosome (6), probably with the assistance of TRAMP.
Figure 5
Figure 5
Comparison of Targets of the Core Exosome and Rrp6 (A) Proportion of sequences corresponding to functional RNA classes recovered with core exosome subunits (Rrp44, Rrp41, Csl4), and Rrp6. Sequencing data was analyzed as in Figure 1. (B) Heat maps for main non-protein coding RNA substrate groups recovered with the indicated IP. Numbers of reads mapped to individual RNAs are shown in shades of red. (C) Read coverage along highly structured RNAs (top) the U2 snRNA (LSR1; 1175nt); (middle) pre-tRNAProUGG (102nt, intron 37-66nt) and (bottom) the box C/D snoRNA snR40 (97nt).
Figure 6
Figure 6
Interactions of Rrp44 and Rrp6 with Pre-mRNA (A) Frequencies of reads mapped to pre-mRNAs and mature mRNAs. IE/EE: Relative numbers of reads mapped to intron-exon junctions (IE) in pre-mRNAs relative to exon-exon junctions (EE) in mature mRNAs. Introns/Total mRNA: Numbers of reads mapped to mRNA introns relative to the total number of reads mapped to mRNAs. 3′SS/5′SS: Relative numbers of reads mapped to 3′ splice sites (3′SS) in pre-mRNAs, relative to 5′ splice (5′SS) junctions. Bars indicate the standard error. (B) Rrp44 and Rrp6 binding profiles (black) along 219 intron-containing pre-mRNAs. Pre-mRNAs are aligned at their 3′ splice sites, and ordered by intron length. Intron boundaries are shown as red lines. (C) Grouping of 4849 mRNAs by pattern of interactions with exosome proteins. Experiments were clustered by complete linkage using the correlation distance metric. Replicate experiments clustered together confirming the reproducibility of the data. Numbers of reads mapped to individual RNAs are shown in shades of red.
Figure 7
Figure 7
Distribution of High-Throughput Sequencing Reads from Core Exosome, Rrp6, and Trf4 Data Sets over the Pre-rRNA and (Pre-)tRNAs (A) Coverage of high-throughput sequencing reads along the 35S pre-rRNA (6.9kb). The peak around 5.8kb in the 25S rRNA is a background contaminant seen in many experiments (Granneman et al., 2009; Granneman et al., 2010; van Nues et al., 2011). (B) Coverage of reads, either unfiltered (total) or filtered for reads containing 2 or more non-templated As (A tails), from Rrp44, Rrp6 and Trf4 data sets were mapped to the 18S rRNA region of the pre-rRNA. (C) The lines indicate 45 different yeast tRNAs (one for each anticodon family). Dashed lines indicate the presence of introns in the pre-tRNAs. The tRNAs are ranked by length (including intron if present) and aligned at the 5′ end of the mature sequence. Read coverage is indicated by color intensity.
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References

    1. Allmang C., Kufel J., Chanfreau G., Mitchell P., Petfalski E., Tollervey D. Functions of the exosome in rRNA, snoRNA and snRNA synthesis. EMBO J. 1999;18:5399–5410. - PMC - PubMed
    1. Bonneau F., Basquin J., Ebert J., Lorentzen E., Conti E. The yeast exosome functions as a macromolecular cage to channel RNA substrates for degradation. Cell. 2009;139:547–559. - PubMed
    1. Briggs M.W., Burkard K.T., Butler J.S. Rrp6p, the yeast homologue of the human PM-Scl 100-kDa autoantigen, is essential for efficient 5.8 S rRNA 3′ end formation. J. Biol. Chem. 1998;273:13255–13263. - PubMed
    1. Callahan K.P., Butler J.S. Evidence for core exosome independent function of the nuclear exoribonuclease Rrp6p. Nucleic Acids Res. 2008;36:6645–6655. - PMC - PubMed
    1. Callahan K.P., Butler J.S. TRAMP complex enhances RNA degradation by the nuclear exosome component Rrp6. J. Biol. Chem. 2010;285:3540–3547. - PMC - PubMed

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