Molecular cloning of rat human type IX collagen cDNA and localization of the α1(IX) gene on the human chromosome 6

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Abstract
Type IX collagen is found in hyaline cartilage, where it is asociated with type II collagen lin quarter-stagered collagen firils. Chicken type IX collagen has been extensively characterized and shown to contain molecules with three tripole-helical domains, interspersed with non-triple-helical sequences. The molecule contains three, genetically disstinct, subunits and one of these subunits carries a covalently bound glycosaminoglycan side chain. In the present report, we describe for the first time the primary structure of mammalian type IX collagen chains, based on cloning and sequencing of cDNA from rat and human cDNA libraries. The results suggest that mammalian α1(IX) chains have the same multi-domain structure as the avian protein. We also demonstrate, by in situ hybridization of chromosome spreads, that the human α1(IX) collagen gene is located on the long arm of chromosome 6. The cloning of human type IX collagon cDNA provides a probe for molecular studies of human chondrodysplasias that may involve abnormalities in this extracellular collagen-proteoglycan.