Exon structure of the gene encoding the human mannose-binding protein-associated serine protease light chain: Comparison with complement C1r and C1s genes

Mannan or mannose-binding protein (MBP) requires a novel serine protease termed MBP-associated serine protease (MASP) for activation of the complement cascade. In this study, we analyzed MASP genomic clones and found that the light chain (catalytic domain) is encoded by six exons, whereas those of the complement C1 subunits, C1r and C1s, and the haptoglobin segment have been reported to be encoded by a single exon. We confirmed the intron-lacking sequence of C1r by analysis of its genome. These results, in conjunction with those obtained by constructing a phylogenetic tree for these proteins, suggest that the MASP gene is a prototype and that the intron-lacking sequences of the other serine proteases have a more recent history.