Schematic representation of the LU gene showing exons and the corresponding structural domains of Lu gp. D1-5 are IgSF domains. In the mRNA species encoding the Lu gp isoform B-CAM, the intron between exons 13 and 14 is not spliced.8 The numbering of nucleotides is as given in the Genbank database entry for Lu gp cDNA, accession number X83425, abbreviations are as in Table 3.