Molecular genetic and structural aspects of MBL. Representation of the gene organization of MBL2 (MBL1 is a pseudogene)and the locations within Exon 1 that most commonly present polymorphisms, resulting in the variant alleles B, C, and D (codons 54, 57, and 52, respectively), in addition to the P/Q variant at position +4 (5'-Unstranslated region). Upstream from Exon 1, the sites of promoter mutations that lead to the H/L and X/Y variants are also demonstrated. The MBL2 gene is comprised of four exons. Exon 1 encodes the serine protease domain (SP) (1), the cysteine-rich region (CRR) (2), and a portion of the collagen-like domain (CLD) (3); exon 2 encodes the remainder of the CLD; exon 3 encodes the neck region (4); and exon 4 encodes the carbohydrate-recognition domain (CRD) (5). Components of the MBL gene that process transcription of these various components of the fully assembled MBL protein are also designated in this cartoon. Location of insert (A) showing mutations on Exon map is represented by black arrow.