RNA recognition motif (RRM)-like Smg4_UPF3 domain in up-frameshift suppressor 3 homolog B on chromosome X (Upf3B)
This subgroup corresponds to the RRM-like Smg4_UPF3 domain in Upf3B, also termed regulator of nonsense transcripts 3B, or nonsense mRNA reducing factor 3B, a human ortholog of yeast Upf3p and Caenorhabditis elegans SMG-4. It derives from X-linked gene UPF3B and is required for nonsense-mediated mRNA decay (NMD) in human. Upf3B is a nucleocytoplasmic shuttling protein that associates selectively with spliced beta-globin mRNA in vivo. Like other Upf3 proteins, Upf3B contains nuclear import and export signals, and a conserved Smg4_UPF3 domain with some similarity to an RNA recognition motif (RRM), indicating that it may be an RNA binding protein.