Spliceosomal snRNPs are multicomponent particles that undergo a complex maturation pathway. Human Sm-class snRNAs are generated as 3'-end extended precursors, which are exported to the cytoplasm and assembled together with Sm proteins into core RNPs by the SMN complex. Here, we provide evidence that these pre-snRNA substrates contain compact, evolutionarily conserved secondary structures that overlap with the Sm binding site. These structural motifs in pre-snRNAs are predicted to interfere with Sm core assembly. We model structural rearrangements that lead to an open pre-snRNA conformation compatible with Sm protein interaction. The predicted rearrangement pathway is conserved in Metazoa and requires an external factor that initiates snRNA remodeling. We show that the essential helicase Gemin3, which is a component of the SMN complex, is crucial for snRNA structural rearrangements during snRNP maturation. The SMN complex thus facilitates ATP-driven structural changes in snRNAs that expose the Sm site and enable Sm protein binding.

• MeSH
• HeLa Cells MeSH
• snRNP Core Proteins genetics   MeSH
• Humans MeSH
• RNA Precursors * metabolism   MeSH
• SMN Complex Proteins metabolism   MeSH
• Ribonucleoproteins, Small Nuclear metabolism   MeSH
• RNA, Small Nuclear * metabolism   MeSH
• Check Tag
• Humans MeSH
• Publication type
• Journal Article MeSH
• Research Support, Non-U.S. Gov't MeSH
• Research Support, N.I.H., Extramural MeSH
• Names of Substances
• snRNP Core Proteins MeSH
• RNA Precursors * MeSH
• SMN Complex Proteins MeSH
• Ribonucleoproteins, Small Nuclear MeSH
• RNA, Small Nuclear * MeSH

ISG20L2, a 3' to 5' exoribonuclease previously associated with ribosome biogenesis, is identified here in activated T cells as an enzyme with a preferential affinity for uridylated miRNA substrates. This enzyme is upregulated in T lymphocytes upon TCR and IFN type I stimulation and appears to be involved in regulating T cell function. ISG20L2 silencing leads to an increased basal expression of CD69 and induces greater IL2 secretion. However, ISG20L2 absence impairs CD25 upregulation, CD3 synaptic accumulation and MTOC translocation towards the antigen-presenting cell during immune synapsis. Remarkably, ISG20L2 controls the expression of immunoregulatory molecules, such as AHR, NKG2D, CTLA-4, CD137, TIM-3, PD-L1 or PD-1, which show increased levels in ISG20L2 knockout T cells. The dysregulation observed in these key molecules for T cell responses support a role for this exonuclease as a novel RNA-based regulator of T cell function.

• Keywords
• Exonuclease, ISG20L2, Immunoregulatory, T cell,
• MeSH
• Lymphocyte Activation * MeSH
• Antigen-Presenting Cells MeSH
• Endonucleases MeSH
• Humans MeSH
• MicroRNAs * genetics   MeSH
• Check Tag
• Humans MeSH
• Publication type
• Journal Article MeSH
• Names of Substances
• Endonucleases MeSH
• MicroRNAs * MeSH

Transfer RNAs acquire a large plethora of chemical modifications. Among those, modifications of the anticodon loop play important roles in translational fidelity and tRNA stability. Four human wobble U-containing tRNAs obtain 5-methoxycarbonylmethyluridine (mcm5U34) or 5-methoxycarbonylmethyl-2-thiouridine (mcm5s2U34), which play a role in decoding. This mark involves a cascade of enzymatic activities. The last step is mediated by alkylation repair homolog 8 (ALKBH8). In this study, we performed a transcriptome-wide analysis of the repertoire of ALKBH8 RNA targets. Using a combination of HITS-CLIP and RIP-seq analyses, we uncover ALKBH8-bound RNAs. We show that ALKBH8 targets fully processed and CCA modified tRNAs. Our analyses uncovered the previously known set of wobble U-containing tRNAs. In addition, both our approaches revealed ALKBH8 binding to several other types of noncoding RNAs, in particular C/D box snoRNAs.

• Keywords
• ALKBH8, HITS-CLIP, Trm9, mcm5U, mcm5s2U, wobble uridine modification,
• MeSH
• AlkB Homolog 8, tRNA Methyltransferase genetics   MeSH
• Anticodon MeSH
• Chromatin Immunoprecipitation Sequencing * MeSH
• Humans MeSH
• RNA, Untranslated genetics   MeSH
• RNA, Transfer * genetics   metabolism   MeSH
• Check Tag
• Humans MeSH
• Publication type
• Journal Article MeSH
• Research Support, Non-U.S. Gov't MeSH
• Names of Substances
• AlkB Homolog 8, tRNA Methyltransferase MeSH
• ALKBH8 protein, human MeSH Browser
• Anticodon MeSH
• RNA, Untranslated MeSH
• RNA, Transfer * MeSH

Spliceosomal small nuclear ribonucleoprotein particles (snRNPs) undergo a complex maturation pathway containing multiple steps in the nucleus and in the cytoplasm. snRNP biogenesis is strictly proofread and several quality control checkpoints are placed along the pathway. Here, we analyzed the fate of small nuclear RNAs (snRNAs) that are unable to acquire a ring of Sm proteins. We showed that snRNAs lacking the Sm ring are unstable and accumulate in P-bodies in an LSm1-dependent manner. We further provide evidence that defective snRNAs without the Sm binding site are uridylated at the 3' end and associate with DIS3L2 3'→5' exoribonuclease and LSm proteins. Finally, inhibition of 5'→3' exoribonuclease XRN1 increases association of ΔSm snRNAs with DIS3L2, which indicates competition and compensation between these two degradation enzymes. Together, we provide evidence that defective snRNAs without the Sm ring are uridylated and degraded by alternative pathways involving either DIS3L2 or LSm proteins and XRN1.

• MeSH
• Exoribonucleases metabolism   MeSH
• HeLa Cells MeSH
• Nucleic Acid Conformation * MeSH
• Humans MeSH
• Organelles metabolism   MeSH
• SMN Complex Proteins metabolism   MeSH
• RNA-Binding Proteins metabolism   MeSH
• Proto-Oncogene Proteins metabolism   MeSH
• RNA, Small Nuclear chemistry   metabolism   MeSH
• Base Sequence MeSH
• RNA Stability MeSH
• RNA Transport * MeSH
• Protein Binding MeSH
• Binding Sites MeSH
• Check Tag
• Humans MeSH
• Publication type
• Journal Article MeSH
• Research Support, Non-U.S. Gov't MeSH
• Names of Substances
• DIS3L2 protein, human MeSH Browser
• Exoribonucleases MeSH
• GEMIN5 protein, human MeSH Browser
• LSM1 protein, human MeSH Browser
• SMN Complex Proteins MeSH
• RNA-Binding Proteins MeSH
• Proto-Oncogene Proteins MeSH
• RNA, Small Nuclear MeSH

Most eukaryotic RNAs are posttranscriptionally modified. The majority of modifications promote RNA maturation, others may regulate function and stability. The 3' terminal non-templated oligouridylation is a widespread modification affecting many cellular RNAs at some stage of their life cycle. It has diverse roles in RNA metabolism. The most prevalent is the regulation of stability and quality control. On the cellular and organismal level, it plays a critical role in a number of pathways, such as cell cycle regulation, cell death, development or viral infection. Defects in uridylation have been linked to several diseases. This review summarizes the current knowledge about the role of the 3' terminal oligo(U)-tailing in biology of various RNAs in eukaryotes and describes key factors involved in these pathways.This article is part of the theme issue '5' and 3' modifications controlling RNA degradation'.

• Keywords
• RNA degradation, RNA modification, RNA processing, RNA surveillance, RNA uridylation, tutase,
• MeSH
• Eukaryota MeSH
• Eukaryotic Cells physiology   MeSH
• Humans MeSH
• RNA metabolism   MeSH
• RNA 3' End Processing * MeSH
• Uridine metabolism   MeSH
• Check Tag
• Humans MeSH
• Publication type
• Journal Article MeSH
• Research Support, Non-U.S. Gov't MeSH
• Review MeSH
• Names of Substances
• RNA MeSH
• Uridine MeSH