SF3A3 is a subunit of the SF3a splicing factor complex required for binding of the U2 snRNP to the pre-mRNA in an early step of spliceosome assembly []. Several SF3A3 homologues are also included in this entry , such as Prp9 from budding yeasts and Sap61 from fission yeasts. In budding yeasts, SF3a complex shows a bifurcated assembly structure of three subunits, Prp9 (subunit 3), Prp11 (subunit 2) and Prp21 (subunit 1). Prp9 and Prp21 were not thought to interact with each other but the alpha1 helix of Prp9 does make important contacts with the SURP2 domain of Prp21, thus the two do interact via a bidentate-binding mode. Prp9 harbours a major binding site for stem-loop IIa of U2 snRNA [].
This entry represents a domain found in the SF3A3 protein, which is s component of the SF3a splicing factor complex of the mature U2 snRNP (small nuclear ribonucleoprotein particle). This domain can also be found in SF3A3 yeast homologues, Prp9 and Sap61.In budding yeasts, SF3a complex shows a bifurcated assembly structure of three subunits, Prp9 (subunit 3), Prp11 (subunit 2) and Prp21 (subunit 1). Prp9 and Prp21 were not thought to interact with each other but the alpha1 helix of Prp9 does make important contacts with the SURP2 domain of Prp21, thus the two do interact via a bidentate-binding mode. Prp9 harbours a major binding site for stem-loop IIa of U2 snRNA [].
The mature U2 snRNP (small nuclear ribonucleoprotein particle) relies on the spliceosome assembly for its function, which involves the Splicing factor 3a (SF3a), an evolutionary eukaryotic conserved heterotrimeric complex, essential for pre-mRNA splicing []. This complex includes three subunits: SF3a60, SF3a66 and SF3a120 in the human complex, being Prp9, Prp11 and Prp21 the counterparts in Saccharomyces cerevisiae. SF3a60 possess a highly conserved C2H2-type zinc-finger domain at the C-terminal, while Prp9 has two such domains; SF3a66 and Prp11 contain one C2H2-type zinc-finger domain and SF3a120/Prp21 has two suppressor-of-white-apricot and prp21/spp91 (SURP) domains, followed by a short segment of charged residues. The SURP2 domain of SF3a120/Prp21 has a role in SF3a60/Prp9 binding, however, SURP1 domain function is unknown. The yeast structure shows that Prp9 interacts with Prp21 via a bidentate-binding mode, and Prp21 is wrapped around Prp11 [].This entry represents the C-terminal region of SF3a60 subunit (also known as SF3a3 and Spliceosome-associated protein 61 or Prp9 from yeast) from SF3a complex, found in eukaryotes. This domain has two conserved sequence motifs: PIP and CEICG. It contains a zinc-finger domain of the C2H2-type which might be important for RNA binding and protein-protein interactions with components of the SF3b complex [].
