UPF1 and viral infectious disease: This antagonistic effect of NMD on viral infections in mammalian cells is also highlighted in recent reports that demonstrate that the NMD proteins UPF1, SMG5 and SMG7 restrict the replication of Semliki Forest virus (SFV) and Sindbis virus of the Togaviridae family and the genomic RNA of SFV was found to be a substrate for NMD, with UPF1 depletion resulting in a nearly 20-fold increase in virus production [51, 56, 58].