This domain family is found in eukaryotes, and is typically between 212 and 238 amino acids in length. The family is found in association with Pfam:PF01805. There are two completely conserved residues (W and H) that may be functionally important. PRP21 is required for assembly of the prespliceosome and it interacts with U2 snRNP and/or pre-mRNA in the prespliceosome. This family also contains proteins similar to PRP21, such as the mammalian SF3a. SF3a also interacts with U2 snRNP from the prespliceosome, converting it to its active form.

1: The Saccharomyces cerevisiae PRP21 gene product is an integral component of the prespliceosome. Arenas JE, Abelson JN; Proc Natl Acad Sci U S A. 1993;90:6771-6775. PMID:8341697

2: Mammalian splicing factor SF3a120 represents a new member of the SURP family of proteins and is homologous to the essential splicing factor PRP21p of Saccharomyces cerevisiae. Kramer A, Mulhauser F, Wersig C, Groning K, Bilbe G; RNA. 1995;1:260-272. PMID:7489498