The zincins are a superfamily of structurally-related Zn(2+)-binding metallopeptidases which play a major role in a wide range of biological processes including pattern formation, growth factor activation and extracellular matrix synthesis and degradation. In this paper we report the identification and complete primary structure of a novel 33 kDa protein which contains the zinc-binding HEXXH motif found in the zincin superfamily. We have named this novel protein PRSM1 (PRoteaSe, Metallo, number 1). The gene was identified by the immunoscreening of a human placental cDNA library using polyclonal antibodies raised to the 70 kDa human matrix metalloendopeptidase, type III procollagen N-proteinase [Halila, R. and Peltonen, L. (1986) Purification of human procollagen type III N-proteinase from placenta and preparation of antiserum. Biochem. J. 239, 47-52]. The protein is found in placenta and cultured osteosarcoma cells. PRSM1 could share sequence homology with the type III procollagen N-proteinase. The prsm1 gene is represented once in the human genome and is localized on chromosome 16 (q24.3).