MOLECULAR-CLONING OF HUMAN GASTRIC MUCIN MUC5AC REVEALS CONSERVED CYSTEINE-RICH D-DOMAINS AND A PUTATIVE LEUCINE-ZIPPER MOTIF

To further clone the human gastric mucin MUC5AC cDNA, we screened a hu man gastric cDNA library with previously identified MUC5AC sequences. We obtained 32 independent clones encoding newly identified sequences comprising the entire N-terminal sequence of MUC5AC, up to 3024 bp ups tream of the previously identified MUC5AC sequences. The N-terminus of MUC5AC shows high homology (43% identity) with the N-terminus of MUC2 and contains three domains homologous to the D-domains found in the p ro-von Willebrand factor. Furthermore, the N-terminus of MUC5AC contai ns a putative leucine zipper motif not found in any other mucin identi fied so far. Moreover, a large central repetitive sequence was identif ied encoding approximately 2500 amino acids (7.5 kb). We were able to establish that the MUC5AC cDNA together with the previously identified 6.1 kb of MUC5AC cDNA sequence is about 16.6 kb, encoding 5525 amino acids. A model of the domain structure of MUC5AC is presented. (C) 199 8 Academic Press.