MOLECULAR-CLONING AND CHARACTERIZATION OF THE GENE ENCODING RAT SUBMANDIBULAR-GLAND APOMUCIN, MUCSMG

Mucin glycoproteins are a major constituent of salivary secretions and play a primary role in the protection of the oral cavity. Rat submand ibular glands (RSMG) synthesize and secrete a low molecular weight (11 4 kDa) mucin glycoprotein. We have isolated, partially sequenced, and characterized the gene which encodes the RSMG apomucin. The gene is en coded by three exons of 106 nt, 69 nt, and 991 nt, separated by intron s of 921 nt and 12.5 kb. CAAT and TATA elements are present, at -68 an d -26, respectively, in the 5' flanking sequence of the RSMG apomucin gene. The tandem repeat domain present in exon III consists of ten tan dem repeats of 39 nt encoding the consensus sequence PTTDSTTPAPTTK. Se quence comparison and organization of the nucleic acid sequence encodi ng the tandem repeats of two alleles for this gene suggests that the a pomucin gene has undergone recombinational events during its evolution . No significant sequence similarity was found with other mucin genes, or with other known salivary gland-specific genes. The gene was local ized to rat chromosome 14 using somatic cell hybrids that segregate ra t chromosomes. Since this, to our knowledge, represents the first RSMG mucin gene cloned, we have designated this gene Mucsmg.