Table 1.

Key NMD factors and their cellular functions in other pathways in animals

Factor in humans	Non-NMD functions in humans	Embryonic lethality*	Other comments	References
UPF1	Staufen (STAU)1- mediated mRNA decay; histone mRNA decay at the end of S phase; DNA replication; telomere maintenance; small RNA-induced mRNA downregulation	Fruitfly, zebrafish, mouse	Called SMG2 in nematode	[17●●,50●●,52,55,62,68–72]
UPF2	Telomere maintenance (minor role relative to UPF1)	Fruitfly, zebrafish, mouse	Called SMG3 in nematode	[17●●,33,58,59●●,69]
UPF3 (UPF3a) or UPF3X (UPF3b)	None reported	None	Called SMG4 in nematode; UPF3a has peripheral role in NMD for most NMD targets in fruitful; no UPF3b orthologue in fruitfly	[14,32, 50●●]
SMG1	DNA-damage response to ionizing radiation; nutrient-dependent signaling; telomere maintenance	Mouse	NMD factor for only certain NMD targets in fruitfly	([33,51,52,57 ●●,69,73]; reviewed in [74])
SMG5, SMG6 and SMG7	Telomere maintenance	Zebrafish	No SMG7 orthologue in fruitfly	[17●●,32,69,72]
NAG/NBAS	Amplified in neuroblastoma	Nematode, zebrafish	Called SMGL-1 in nematode; no orthologue in fruitfly	[35,54●●]
DHX34	Putative ATP-dependent RNA helicase that probably functions in non-NMD pathways	Nematode, zebrafish	Called SMGL-2 and CG32533 in nematode and fruitfly, respectively	([35,54●●]; reviewed in [75])

^*when downregulated (nematode or zebrafish) or completely absent (fruitfly, mouse)