All eukaryotes that have been studied to date possess the ability to detect and degrade transcripts that contain a premature signal for the determination of translation. This process of nonsense-mediated RNA decay (NMRD) has been most comprehensively studied in the yeast Saccharomyces cerevisiae where at least three trans-acting factors (Upf1p through Upf3p) are required. The present invention provides cDNAs encoding human and murine RENT1(regulator of nonsense transcripts). RENT1 is the first identified mammalian protein that contains all of the putative functional elements in Upf1p including zinc finger-like motifs and NTPase domains as well as all motifs common to members of helicase superfamily I. Moreover, expression of a chimeric protein, containing the central region of RENT1 flanked by the extreme N- and C-termini of Upf1p, complements the Upf1p-deficient phenotype in yeast.