Abstract
Splicing of precursor mRNA takes place via two consecutive steps of transesterification catalyzed by a large ribonucleoprotein complex called the spliceosome. The spliceosome is assembled through ordered binding to the pre-mRNA of five small nuclear RNAs and numerous protein factors, and is disassembled after completion of the reaction to recycle all components. Throughout the splicing cycle, the spliceosome changes its structure, rearranging RNA-RNA, RNA-protein and protein-protein interactions, for positioning and repositioning of splice sites. DExD/H-box RNA helicases play important roles in mediating structural changes of the spliceosome by unwinding of RNA duplexes or disrupting RNA-protein interactions. DExD/H-box proteins are also implicated in the fidelity control of the splicing process at various steps. This review summarizes the functional roles of DExD/H-box proteins in pre-mRNA splicing according to studies conducted mostly in yeast and will discuss the concept of the complicated splicing reaction based on recent findings.
Highlights
RNA splicing is a fundamental process in eukaryotic gene expression and is highly regulated in higher eukaryotic cells
Spp2 was previously shown to be required for the recruitment of Prp2 to the spliceosome, a recent study using a purified splicing system revealed that Spp2 is dispensable for Prp2 recruitment, but functions in coupling the ATPase activity of Prp2 to remodeling of the spliceosome into a catalytically active form [89]
Genetic data showed that Prp8-Arg1753 mutants suppress Prp22 helicase-defective mutants [113] as well as specific U5 loop 1 mutant alleles [114]. These results suggest that Prp8-Arg1753 may play a role in stabilizing U5/exon interactions before exon ligation, and Prp22 may function in disrupting RNA-RNA or RNA-protein interactions that are normally stabilized by Prp8
Summary
RNA splicing is a fundamental process in eukaryotic gene expression and is highly regulated in higher eukaryotic cells. Prp5 was previously proposed to play a role in splicing fidelity control to proofread the branch site by competing with base pairing between U2 snRNA and the branch site sequence in an ATP-dependent manner [39, 40]. A recent report reveals an alternative mechanism for Prp5 functions in proofreading the branch site sequence by counteracting tri-snRNP binding independent of ATP [40].
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