This entry represents the RNA recognition motif (RRM) of the Ist3 family that includes fungal Ist3 (also known as SNU17), X-linked 2 RNA-binding motif proteins (RBMX2) found in Metazoa and plants, and similar proteins. Ist3 is a novel yeast Saccharomyces cerevisiae protein required for the first catalytic step of splicing and for progression of spliceosome assembly []. It binds specifically to the U2 snRNP and is an intrinsic component of prespliceosomes and spliceosomes [, , ].Yeast Ist3 contains an atypical RNA recognition motif (RRM), also termed RBD (RNA binding domain) or RNP (ribonucleoprotein domain). In the yeast pre-mRNA retention and splicing complex, the atypical RRM of Ist3 functions as a scaffold that organizes the other two constituents, Bud13 (bud site selection 13) and Pml1 (pre-mRNA leakage 1) []. The biological function of RBMX2 remains unclear. It shows high sequence similarity to yeast ist3 protein and harbours one RRM as well.
