Participates in pre-mRNA splicing. Part of the U4/U5/U6 tri-snRNP complex, one of the building blocks of the spliceosome (By similarity). Essential for reproduction. In female gametophyte, is necessary for the egg cell and central cell fate determination and hence reproductive success. Involved in a mechanism that prevents accessory cells from adopting gametic cell fate (PubMed:17326723). Modulates egg cell signaling center that regulates the development of all female gametophytic cells (PubMed:22190635). Colocalizes with CLO. During female gametophyte development, preferentially expressed in the gametic cells. Gametophytic lethality due to female gametophyte defect, when homozygous.