mda-5, but not RIG-I, is a common target for paramyxovirus V proteins.

The induction of IFN-beta by the paramyxovirus PIV5 (formerly known as SV5) is limited by the action of the viral V protein that targets the cellular RNA helicase mda-5. Here we show that 12 other paramyxoviruses also target mda-5 by a direct interaction between the conserved cysteine-rich C-terminus of their V proteins and the helicase domain of mda-5. The inhibition of IFN-beta induction is not species-restricted, being observed in a range of mammalian cells as well as in avian cells, and we show that the inhibition of mda-5 function is also not restricted to mammalian cells. In contrast, the V proteins do not bind to the related RNA helicase RIG-I and do not inhibit its activity. The relative contributions of mda-5 and RIG-I to IFN-beta induction are discussed.