Involved in pre-mRNA splicing. Required for the assembly of the U4/U5/U6 tri-snRNP complex, one of the building blocks of the spliceosome (By similarity). Functions in association with STA1 and ZOP1 in spliceosome dynamics and pre-mRNA splicing. Required for transcriptional regulation and pre-mRNA splicing of cold-responsive genes, such as LTI78/RD29A, KIN2/COR6.6 or COR15A, especially under cold stress. May play a role in stress response. Involved in transcriptional gene silencing of endogenous transposable elements, independently of the RNA-directed DNA methylation (RdDM) pathway. Seems not to participate in the small RNA biogenesis of the RdDM pathway (PubMed:25684655). Component of the U4/U6-U5 tri-snRNP complex composed of the U4, U6 and U5 snRNAs and pre-mRNA-splicing factors (By similarity). Interacts with STA1 and SOP1 (PubMed:25684655). Developmental defects, semi-dwarf phenotype and reduced growth. Belongs to the PRP31 family.