CLONING AND COMPLETE PRIMARY STRUCTURE OF THE MOUSE LAMININ ALPHA-3 CHAIN - DISTINCT EXPRESSION PATTERN OF THE LAMININ ALPHA-3A AND ALPHA-3B CHAIN ISOFORMS

We have isolated and characterized overlapping cDNA clones encoding the alpha 3A and alpha 3B chains of mouse laminin 5. Sequence analysis of the cDNA for the alpha 3B predicts a polypeptide of 2541 amino acids (279,510 Da) comprising a truncated short arm and a carboxyl-terminal long arm common to the laminin a chains identified thus far. The short arm of the alpha 3B chain harbors two alternating epidermal growth factor-like domains and two globular domains. The amino-terminal globular domain, thought to mediate interactions with molecules of the extracellular matrix, shows no significant homology to any globular domain at the tips of the known laminin isoforms. The alpha 3A cDNA predicts a polypeptide of 1711 amino acids (186,230 Da) that substitutes a short sequence of 43 amino acids for the short arm seen in the alpha 3B isoform and displays 77% conservative homology to the alpha 3Ep chains of the adhesion ligand epiligrin. Northern and Western blot analyses of skin and lung epithelial cells demonstrated the tissue-specific expression of the laminin alpha 3A and alpha 3B isoforms, and in situ hybridization on mouse embryos revealed a focal localization of alpha 3B in areas of the central nervous system.