DNA/RNA helicase Upf1 seems to interact with axonal transcripts in response to nerve growth factor (NGF, A. Ludanyi, M. Gaspari and A. Riccio, unpublished data). In order to shed light on Upf1 mechanism of action and to identify potential associations with molecules having cleavage activity, we performed an AP-MS experiment comprising Upf1 immunoprecipitation, on-beads digestion, isotopic labelling (18O) and quantitative LC-MS/MS analysis.