Characterization of the biochemical properties of the human Upf1 gene product that is involved in nonsense-mediated mRNA decay

The Upf1 protein in yeast has been implicated in the modulation of efficien t translation termination as well as in the accelerated turnover of mRNAs c ontaining premature stop codons, a phenomenon called nonsense-mediated mRNA decay (NMD). A human homolog of the yeast UPF1, termed HUpf1/RENT1, has al so been identified. The HUpf1 has also been shown to play a role in NMD in mammalian cells. Comparison of the yeast and human UPF1 proteins demonstrat ed that the amino terminal cysteine/histidine-rich region and the region co mprising the domains that define this protein as a superfamily group I heli case have been conserved. The yeast Upf1p demonstrates RNA-dependent ATPase and 5' --> 3' helicase activities. In this paper, we report the expression , purification, and characterization of the activities of the human Upf1 pr otein. We demonstrate that human Upf1 protein displays a nucleic-acid-depen dent ATPase activity and a 5' --> 3' helicase activity. Furthermore, human Upf1 is an RNA-binding protein whose RNA-binding activity is modulated by A TP. Taken together, these results Indicate that the activities of the Upf1 protein are conserved across species, reflecting the conservation of functi on of this protein throughout evolution.