Plays a role in mRNA splicing as a component of the U4/U6-U5 tri-snRNP, one of the building blocks of the spliceosome. May also bind to DNA. Appears to play a role in hypoxia-induced regulation of EPO gene expression. Identified in the spliceosome C complex. Component of the U4/U6-U5 tri-snRNP complex composed of the U4, U6 and U5 snRNAs and at least PRPF3, PRPF4, PRPF6, PRPF8, PRPF31, SNRNP200, TXNL4A, SNRNP40, DDX23, CD2BP2, PPIH, SNU13, EFTUD2, SART1 and USP39 (By similarity). Ubiquitously expressed. Shows a high expression in fetal liver and a low expression in adult liver. Expressed at maximal level at 12 dpc. Declines progressively until birth. Sumoylated with SUMO2. Belongs to the SNU66/SART1 family.