UPF3B
Description
The UPF3B (UPF3B regulator of nonsense mediated mRNA decay) is a protein-coding gene located on chromosome X.
Regulator of nonsense transcripts 3B is a protein that in humans is encoded by the UPF3B gene. This gene encodes a protein that is part of a post-splicing multiprotein complex involved in both mRNA nuclear export and mRNA surveillance. The encoded protein is one of two functional homologs to yeast Upf3p. mRNA surveillance detects exported mRNAs with truncated open reading frames and initiates nonsense-mediated mRNA decay (NMD). When translation ends upstream from the last exon-exon junction, this triggers NMD to degrade mRNAs containing premature stop codons. This protein binds to the mRNA and remains bound after nuclear export, acting as a nucleocytoplasmic shuttling protein. It forms with Y14 a complex that binds specifically 20 nt upstream of exon-exon junctions. This gene is located on the long arm of chromosome X. Two splice variants encoding different isoforms have been found for this gene.
== Interactions == UPF3B has been shown to interact with UPF2 and UPF1.
UPF3B participates in the nonsense-mediated decay (NMD) pathway, which degrades mRNAs containing premature stop codons. It achieves this by associating with the nuclear exon junction complex (EJC) and acting as a bridge between the EJC core and the NMD machinery. UPF3B recruits UPF2 to the cytoplasmic side of the nuclear envelope, leading to the formation of a UPF1-UPF2-UPF3 surveillance complex (including UPF1 bound to release factors at the stalled ribosome). This complex is believed to activate NMD. In collaboration with UPF2, UPF3B enhances both the ATPase and RNA helicase activities of UPF1. Furthermore, UPF3B binds spliced mRNA upstream of exon-exon junctions. In vitro studies have shown that UPF3B stimulates translation, independent of its association with UPF2 and components of the EJC core.
UPF3B is also known as HUPF3B, MRX62, MRX82, MRXS14, RENT3B, UPF3BP1, UPF3BP2, UPF3BP3, UPF3X, Upf3p-X.
