A Repetitive Structure in the Chick 2-Collagen Gene

The collagens are a family of proteins that constitute the major protein component of the extracellular matrix in animal tissues (for reviews, see Ramachandran and Reddi 1976; Prockop et al. 1979a,b; Eyre 1980). At least five distinct types of collagen are found, all of which show a similar overall structure. The major features of this characteristic structure include the following: presence of glycine residues every third amino acid; abundance of prolines and lysines, many of which are hydroxylated; characteristic configuration of the molecule composed of three subunits that interact with each other to form a triple helical structure; presence of many inter- and intramolecular covalent cross-links resulting in a higher-order structural organization. The primary structure of the collagens varies, however, and probably reflects their different tissue-related functions. It is very likely that the synthesis of each of the collagens responds to a specific tissue-related differentiation program.