SMG9 (SMG9 Nonsense Mediated MRNA Decay Factor) is a protein coding gene that is involved in several pathways such as gene expression and viral mRNA translation. SMG9 serves as a component of the Nonsense Mediated Decay (NMD) process, which is a transcriptional regulatory mechanism that degrades transcripts with premature stop codons. The SMG9 protein has been shown to interact with other components of the NMD machinery to form the SURF complex. This complex is integral for the activation of the protein UPF1, which in turn halts translation at premature stop codons.
Mutations in most genes involved in NMD are associated with embryonic lethality or major malformation syndromes. Mutations in SMG9 have been shown to cause Heart and Brain Malformation Syndrome.