HUMAN MUCIN GENES MUC2, MUC3, MUC4, MUC5AC, MUC5B, AND MUC6 EXPRESS STABLE AND EXTREMELY LARGE MESSENGER-RNAS AND EXHIBIT A VARIABLE-LENGTHPOLYMORPHISM - AN IMPROVED METHOD TO ANALYZE LARGE MESSENGER-RNAS

Of the nine mucin genes that have been characterized, only MUC1 and MU C7 have been fully sequenced, and their transcripts can be detected as distinct bands of predicted size by Northern blot analysis. In contra st, the RNA patterns observed for each of the other MUC genes have usu ally shown a very high degree of polydispersity. This polydispersity h as been believed to be one of the typical features of the mucin mRNAs, but until now, its origin has remained unexplained, In the work descr ibed in the present paper, we investigated two possible kinds of expla nation for this phenomenon: namely that the extensive polydispersity r esults from a biological mechanism or that it is artifactual in origin . The data obtained, as a result of improving the purification and blo tting methods, allowed us to show that in all of the tissues analyzed, each of the genes, MUC2-6, expresses mRNAs that are stable and are of an unusually large size to be found in eukaryotes (14-24 kilobases), Moreover, allelic variations in length of these mucin transcripts were observed, We demonstrate that these variations are directly related t o the variable number of tandem repeat polymorphisms seen at the DNA l evel.