A NOVEL GENE EXPRESSED IN FIAT AMELOBLASTS CODES FOR PROTEINS WITH CELL-BINDING DOMAINS

Two variants of an mRNA sequence are identified that are expressed at high levels in rat ameloblasts during the formation of the enamel matr ix, The sequences contain open reading frames for 407 and 324 amino ac id residues, respectively, The encoded proteins, which we call amelins , are rich in proline, glycine, leucine, and alanine residues and cont ain the peptide domain DGEA, an integrin recognition sequence, The seq uences coding for the C-terminal 305 amino acid residues, the 3' nontr anslated part, and a microsatellite repeat at the nontranslated 5' reg ion are identical in both mRNA variants. The remaining 5' regions cont ain 338 nucleotides unique to the long variant, 54 common nucleotides, and 46 nucleotides present only in the short variant, Eleven nucleoti des have the potential to code for 5 amino acids of both proteins in d ifferent reading frames, The reading frame of the longer variant inclu des codons for a typical N-terminal signal peptide, The amelins are li kely to be constituents of the enamel matrix and the only proteins tha t have so far been implicated in binding interactions between the amel oblast surface and its extracellular matrix.