The core polypeptide of cystic fibrosis tracheal mucin contains a tandem repeat structure. Evidence for a common mucin in airway and gastrointestinal tissue.

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Abstract
A cystic fibrosis trachea cDNA library was constructed and probed with a synthetic oligonucleotide containing a consensus sequence recently identified in human intestinal mucin. One of the isolated clones, AMN-22, has been characterized extensively. The cDNA sequence of this 884-bp fragment was determined, and revealed a tandem repeat structure rich in threonine and proline residues. The repeating sequence of AMN-22 was similar but not identical to that determined for gut mucin. When examined by Northern analysis, the mRNA hybridizing to AMN-22 is extremely polydisperse in cystic fibrosis (CF) trachea, with apparent message length varying from approximately 2 kb to greater than 10 kb. A similar pattern was observed, with less abundant message, in CF bronchiectatic lung parenchyma. The lung cDNA hybridized to a similarly polydisperse message in ulcerative colitis colon RNA, but did not hybridize to control RNA from U937 lymphoma cells or stomach RNA. Pedigree analysis of restriction digests of genomic DNA revealed a pattern indicating a single polymorphic locus for the mucin gene expressed in the lung and the intestine. Southern analyses of human:mouse somatic cell hybrid cell lines allow a chromosomal localization for the mucin gene to human chromosome II, within the region 11p13-11pTer. Taken together, these data demonstrate that a polymorphic gene encodes a mucin core polypeptide expressed in both lung and intestine.