Smg-9 Homolog (SMG9)

Using reciprocal immunoprecipitation analysis, Yamashita et al. (2009) showed that SMG8 and SMG9 tightly associated with SMG1 in HeLa cell lysates, and that SMG9 appeared to mediate the interaction. Both SMG8 and SMG9 suppressed the kinase activity of SMG1, and both were SMG1 target substrates. Depletion of SMG9 resulted in accumulation of phosphorylated UPF1. SMG8 was required to recruit SMG1 to the surveillance complex, and depletion of SMG8 caused accumulation of a complex containing the ribosome, UPF1, ERF1, ERF3, and the EJC on the spliced mRNA-protein complex. The deduced 520-amino acid protein has a central NTPase domain and is highly conserved in many metazoans, but not in yeast or Arabidopsis thaliana. SMG9 had an apparent molecular mass of 60 kD by SDS-PAGE.