N23K, a gene transiently up-regulated during neural differentiation, encodes a precursor protein for a newly identified neuropeptide nociceptin.

We used a subtraction cloning approach to isolate a cDNA of N23K, whose mRNA and protein are transiently up-regulated in mouse NS20Y cells undergoing neurite outgrowth induced by treatment of dibutyryl cyclic AMP. N23K encodes a precursor protein for a newly discovered rat neuropeptide nociceptin. As with other neuropeptide precursors, the N23K protein contains a putative signal peptide rich in hydrophobic amino acids at the N-terminus. N23K mRNA is present only in brain and spinal cord in adult mouse, and is expressed at higher levels in early postnatal brain. These findings suggest that the N23K protein functions not only as a neuropeptide precursor but also as an important component in neuronal differentiation.