Molecular basis of the polydispersity of mucins: Implications for the generation of saccharide diversity.

Secreted epithelial mucins are large macromolecules which exhibit extreme p olydispersity, the molecular basis of which is not fully understood. We hav e obtained partial sequences of two genes (BSM1 and BSM2) coding for two di stinct molecules. This is the first time that such closely-related genes ha ve been identified for any mucin from an animal. We propose that a combinat ion of multiple homologous genes, alternative splicing, differential glycos ylation, and additional post-translational processing all contribute to the extreme polydispersity of mucins. The multiple domain structure and non-id entical tandem repeats are also very important for the generation of the sa ccharide diversities of mucins.