Multiple transcripts of MUC3: Evidence for two genes, MUC3A and MUC3B

The MUC3 gene encodes a transmembrane mucin-type glycoprotein, A number of consistent single nucleotide changes were observed in different MUC3 cDNAs from a single individual, suggesting the presence of at least three differe nt transcripts per individual, This transcript heterogeneity is due both to the existence of a second copy of the MUC3 gene and to allelic changes. Se quencing of the second MUC3 shows that it has the same C-terminal domain an d intron/exon structure as the previously described MUC3, The tandem repeat domain has the same amino acid consensus sequence but shows more substitut ions, The unique exonic sequences range from 94 to 100% identity at the nuc leotide level and correspondingly few amino acid changes have been identifi ed. The introns show around 95% identity. We propose to name this second ge ne MUC3B, MUC3A being reserved for the first MUC3 gene. MUC3B, like MUC3A, is expressed in intestine and Caco-2 cells. (C) 2000 Academic Press.