The helicase activity is required to unwind the RNA-DNA duplex and ATP serves as the energy supply for the helicase activity. Following this unwinding, the released RNA gets trapped and degraded by a complex of various other molecules in P-bodies.
UPF1 has small levels of nuclear localization although it is primarily cytoplasmic. The older concept stated the role of UPF1 in unwinding of dna/rna following which perinuclearly expressed UPF2 interaction and UPF3a/b interaction transports the mRNAs into P bdies for degradation. However, over the time, the complete scenario has changed. The helicase activity is currently believed to be involved in unwinding of an mRNP bound to the RNA.