This family consists of several U1 small nuclear ribonucleoprotein C (U1-C) proteins. The U1 small nuclear ribonucleoprotein (U1 snRNP) binds to the pre-mRNA 5' splice site (ss) at early stages of spliceosome assembly. Recruitment of U1 to a class of weak 5' ss is promoted by binding of the protein TIA-1 to uridine-rich sequences immediately downstream from the 5' ss. Binding of TIA-1 in the vicinity of a 5' ss helps to stabilise U1 snRNP recruitment, at least in part, via a direct interaction with U1-C, thus providing one molecular mechanism for the function of this splicing regulator [1]. This domain is probably a zinc-binding. It is found in multiple copies in some members of the family.

1: The splicing regulator TIA-1 interacts with U1-C to promote U1 snRNP recruitment to 5' splice sites. Forch P, Puig O, Martinez C, Seraphin B, Valcarcel J; EMBO J 2002;21:6882-6892. PMID:12486009