The RES complex is required for efficient transformation of the precatalytic B spliceosome into an activated B^act complex

Abstract

The precise function of the trimeric retention and splicing (RES) complex in pre-mRNA splicing remains unclear. Here we dissected the role of RES during the assembly and activation of yeast spliceosomes. The efficiency of pre-mRNA splicing was significantly lower in the absence of the RES protein Snu17, and the recruitment of its binding partners, Pml1 (pre-mRNA leakage protein 1) and Bud13 (bud site selection protein 13), to the spliceosome was either abolished or substantially reduced. RES was not required for the assembly of spliceosomal B complexes, but its absence hindered efficient B complex formation. ΔRES spliceosomes were no longer strictly dependent on Prp2 activity for their catalytic activation, suggesting that they are structurally compromised. Addition of Prp2, Spp2, and UTP to affinity-purified ΔRES B or a mixture of B/B complexes formed on wild-type pre-mRNA led to their disassembly. However, no substantial disassembly was observed with ΔRES spliceosomes formed on a truncated pre-mRNA that allows Prp2 binding but blocks its activity. Thus, in the absence of RES, Prp2 appears to bind prematurely, leading to the disassembly of the ΔRES B complexes to which it binds. Our data suggest that Prp2 can dismantle B complexes with an aberrant protein composition, suggesting that it may proofread the spliceosome's RNP structure prior to activation.

Bud13 Promotes a Type I Interferon Response by Countering Intron Retention in Irf7

“…In connection with the RES complex, ScBud13 is thought to safeguard formation of the ‘B act complex’ of the spliceosome. 24 In the B act stage, the 5’ splice donor and branch point are recognized by the spliceosome. However, progression to catalysis of the first step of the splicing reaction requires remodeling of several spliceosome components.…”

“…It has been hypothesized that ScBud13 and the RES complex temporally regulate Prp2 binding. 24 In the mammalian context, short, GC-rich introns with weak donor sites may be particularly susceptible to Prp2-mediated disassembly, which may explain the specificity of IR events upon Bud13 depletion.…”

“…Cryo-EM studies, as well as single molecule studies, would seem to suggest compositional heterogeneity of the spliceosome, and that the Bud13-endowed spliceosome may catalyze the splicing reaction in a fundamentally different way than is used in its absence. 24,29,30…”

AtBUD13 affects pre‐mRNA splicing and is essential for embryo development in Arabidopsis

“…In yeast, the RES complex consists of bud‐site selection protein 13 (Bud13p), snRNP‐associated protein 17/Increased sodium tolerance protein 3 (Snu17p/Ist3p) and Pre‐mRNA‐leakage protein 1 (Pml1p); their homologs in human are hBUD13/MGC13125, RNA binding motif protein X‐linked 2 (RBMX2) and Smad nuclear‐interacting protein 1 (SNIP1), respectively (Dziembowski et al ., ; Wysoczanski et al ., ). The yeast RES complex bind to the introns of pre‐mRNAs by the RNA recognition motif (RRM) of Snu17p and interact with the components of the spliceosome to activate the B complex, by which it functions in pre‐mRNA splicing (Dziembowski et al ., ; Schneider et al ., ; Bao et al ., ). Yeast Bud13p interacts directly with Snu17p (Wysoczanski et al ., ); however, it does not interact with Pml1p (Trowitzsch et al ., ; Brooks et al ., ; Wysoczanski et al ., , ; Wysoczanski and Zweckstetter, ; Yan et al ., ).…”

“…So far, the splicing of four pre‐mRNAs, Actin , TAN1 , MER1 and MATa1 , has been demonstrated to be controlled by Bud13p (Clark et al ., ; Khanna et al ., ; Zhou et al ., ; Wysoczanski and Zweckstetter, ; Xu et al ., ). Additionally, Bud13p has been shown to function in the formation of spliceosome and activation of the B complex (Deckert et al ., ; Bessonov et al ., ; Bao et al ., ). However, homologs of Bud13p have not been identified in plants.…”