Recently we described that genetic sequences in the immediately upstream region of the c-fes/fps proto-oncogene, designated fur, constituted a transcription unit for a 4.5-kb mRNA. Here we present characteristics of the genetic organization of fur and some features of its putative translation product which we call furin. The nucleotide sequence of a 3.1-kbp fur-specific cDNA isolated from a human cDNA library revealed an open reading frame of 1,498 bp from which the 499 carboxy-terminal amino acids of the primary fur translational product could be deduced. Computer analysis indicated that furin contained a possible transmembrane domain which resembled that of class II MHC antigens. Furthermore, a cysteine-rich region was present. Significant homology, especially with respect to the topography of cysteine residues, was found between the cysteine-rich regions of the human insulin receptor, the human epidermal growth factor receptor and furin. From the data presented here we deduce that fur may encode a membrane-associated protein with a recognition function.