Cloning, characterization, and tissue expression pattern of mouse tuftelin cDNA

Tuftelin is a protein that has been suggested to function during enamel crystal nucleation. Published sequences for bovine tuftelin cDNA and genomic clones proposed different reading frames that radically affected the derived amino acid sequence of the tuftelin carboxylterminus. We have isolated and characterized a full-length mouse cDNA clone and a partial porcine cDNA clone that include the region of the proposed frame-shift. The mouse tuftelin clone is 2572 nucleotides in length, exclusive of the poly(A+) tail. Translation from the 5′-most ATG yields a protein of 390 amino acids with an isotope-averaged molecular mass of 44.6 kDa and an isoelectric point of 5.9. Comparison of the bovine, mouse, and porcine cDNAs supports the revised bovine tuftelin amino acid sequence and suggests that the bovine tuftelin translation initiation codon be re-assigned to a more 5′ ATG. Re-assigning the translation initiation codon lengthens the tuftelin protein by 52 amino acids, 51 of which are identical between bovine and mouse. At the carboxyl-terminus, the revised bovine and the mouse sequences match at 39 of the final 42 amino acid positions, compared with 2 identities with the originally published bovine reading frame. Northern blot analysis reveals that tuftelin is not ameloblast-specific but is expressed in multiple tissues, including kidney, lung, liver, and testis. Two tuftelin RNA messages, of 2.6 and 3.2 kb, were detected. DNA sequence characterization of an RT-PCR amplification product confirmed expression of tuftelin in kidney, and identified an alternatively spliced mouse tuftelin mRNA lacking exon 2.