Neuroserpin (PI12), initially identified as an axonally secreted protein in cultured chicken dorsal root ganglion neurons, belongs to the serpin family of the serine protease inhibitors and is mainly expressed by neurons of both the developing and the adult nervous system. Here we report on the cloning and structural characterization of the neuroserpin gene of the mouse. The murine neuroserpin gene spans over more than 55kb and consists of nine exons. The positions and phases of the exon¿ntron borders are completely conserved between neuroserpin and its nearest homologues, protease nexin-1 and plasminogen activator inhibitor-1. A single transcription initiation site, which is colocalized with a potential initiation (Inr) sequence, has been determined by primer extension and RNase protection. Sequence analysis revealed a TATA-less promoter with a CAAT box and several sites for the general transcription factor Sp1 and the neuron-specific transcription factor AP-2.