The central domain of bovine submaxillary mucin consists of over 50 tandemrepeats of 329 amino acids - Chromosomal localization of the BSM1 gene andrelations to ovine and porcine counterparts

We previously elucidated five distinct protein domains (I-V) for bovine sub maxillary mucin, which is encoded by two genes, BSM1 and BSM2. Using Southe rn blot analysis, genomic cloning and sequencing of the BSM1 gene, we now s how that the central domain (V) consists of approximate to 55 tandem repeat s of 329 amino acids and that domains III-V are encoded by a 58.4-kb exon, the largest exon known for all genes to date. The BSM1 gene was mapped by f luorescence in situ hybridization to the proximal half of chromosome 5 at b ands q2.2-q2.3. The amino-acid sequence of six tandem repeats (two full and four partial) were found to have only 92-94% identities. We propose that t he variability in the amino-acid sequences of the mucin tandem repeat is im portant for generating the combinatorial library of saccharides that are ne cessary for the protective function of mucins. The deduced peptide sequence s of the central domain match those determined from the purified bovine sub maxillary mucin and also show 68-94% identity to published peptide sequence s of ovine submaxillary mucin. This indicates that the core protein of ovin e submaxillary mucin is closely related to that of bovine submaxillary muci n and contains similar tandem repeats in the central domain. In contrast, t he central domain of porcine submaxillary mucin is reported to consist of 8 1-amino-acid tandem repeats. However, both bovine submaxillary mucin and po rcine submaxillary mucin contain similar N-terminal and C-terminal domains and the corresponding genes are in the conserved linkage regions of the res pective genomes.