RNA recognition motif (RRM) found in U2 small nuclear ribonucleoprotein auxiliary factor U2AF 35 kDa subunit (U2AF35) and similar proteins
This subfamily corresponds to the RRM in U2 small nuclear ribonucleoprotein (snRNP) auxiliary factor (U2AF) which has been implicated in the recruitment of U2 snRNP to pre-mRNAs. It is a highly conserved heterodimer composed of large and small subunits; this family includes the small subunit of U2AF (U2AF35 or U2AF1) and U2AF 35 kDa subunit B (U2AF35B or C3H60). U2AF35 directly binds to the 3' splice site of the conserved AG dinucleotide and performs multiple functions in the splicing process in a substrate-specific manner. It promotes U2 snRNP binding to the branch-point sequences of introns through association with the large subunit of U2AF (U2AF65 or U2AF2). Although the biological role of U2AF35B remains unclear, it shows high sequence homolgy to U2AF35, which contains two N-terminal zinc fingers, a central RNA recognition motif (RRM), also termed RBD (RNA binding domain) or RNP (ribonucleoprotein domain), and a C-terminal arginine/serine (SR) -rich segment interrupted by glycines. In contrast to U2AF35, U2AF35B has a plant-specific conserved C-terminal region containing SERE motif(s), which may have an important function specific to higher plants.