Rat dentin matrix protein 3 is a compound protein of rat dentin sialoprotein and phosphophoryn

During cloning of the rat incisor phosphophoryn gene, several clones were identified with a PP antibody. One of the clones (2PP) was shown to encode a PP denoted as dentin matrix protein 2, DMP2. We have now sequenced another clone, which appears to be bifunctional, or at minimum, has two distinct domains. The 5' region encodes for dentin sialoprotein (DSP), while the 3' region encodes a small or 'mini' PP. There is no stop codon between these domains. The whole gene has been named Dmp3, in keeping with the current nomenclature adopted in our laboratory. The previously reported Dmp2 gene does not encode a DSP domain but has a 114 amino acid carboxy terminal sequence identical except for a single residue with that of the DMP3. Thus, Dmp2, Dmp3 and their corresponding proteins, probably represent related members of a multigene family. There is no evidence for differential splicing. Since the DSP isolated from dentin does not carry the mini-PP domain, it must be cleaved postranslationally from DMP3.