ABSTRACT
T he human Upf (hUpf) proteins work at the core of the nonsense-mediated mRNA decay (NMD) pathway. The three hUpf proteins, hUpfl, hUp£2 and hUpf3, form the hUpf complex, which is critical for the recognition and degradation of mRNAs containing premature termination codons (PTCs). The recognition of PTC-containing mRNAs by the hUpf complex in mammalian cells is promoted by the splicing dependent exon-junction complex (EJC), with which hUpf3 interacts. Following the recognition of PTCs, the hUpf complex is believed to disrupt mRNP structure to prevent further translation and trigger mRNA decay. Emerging evidence suggests that hSmg proteins involved in phosphorylation and de phosphorylation of hUpfl may play a key role in delivering PTC-containing mRNAs to the mRNA decay machinery.
