Nonsense-mediated mRNA decay(NMD) is a RNA surveillance mechanism that detects the mRNAs harboring premature termination condons(PTC),and triggers the degradation to prevent the accumulation of truncated and potentially harmful proteins. NMD also regulates a subset of wild-type physiological transcripts, indicating that NMD plays an important biological role in eukaryotic cells. The key of NMD pathway is PTC recognition from authentic stop condons during translation. Here we reviewed three models to elucidate different mechanisms found in mammals and invertebrates. The NMD effectors such as UPF1（up-frameshift） are involved in the “functional complex” assembly on PTC containing mRNA, although the details of sequential events remain to be clarified for the variety among different organisms, we present the latest progress in postPTC recognition events to better understand the molecular mechanism of NMD pathway.
