Activity of a Chick Collagen Gene in Heterologous and Homologous Cell-Free Extracts

Abstract

The collagens are a family of proteins found in most animal tissues, where they play various important structural roles as extracellular matrix constituents. Type I collagen, which consists of one α2 and two αl polypeptide chains, is a prevalent protein in bone, tendon, and skin (Ramachandran and Reddi, 1976) and is enriched in cultured chick embryo fibroblasts (CEF). We have used CEF in culture as a model system to study the regulation of type I collagen synthesis. The gene coding for α2 (type I) collagen, isolated in a series of overlapping genomic clones, is approximately 38 kilobases long (Ohkubo et al., 1980; Vogeli et al., 1981; Wozney et al., 1981). Figure 1 shows that the coding information in this gene is subdivided into more than 50 exons. The transcription start site at the extreme 5′ end of the α2 collagen gene has been located (Vogeli et al., 1981) and subcloned into the plasmid pBR322 (see Section 2). Residing upstream of the start site (+ 1) are a TATA box (− 33), a CAT box (− 84), and three inverted repeat sequences that have the potential to form hairpin-loop structures (Fig. 2). The sequences involved in the formation of these three dyads of symmetry overlap and are thus mutually exclusive. Depending on which structure is formed, the CAT box is localized in different regions of the hairpin (Fig. 2, A–C). These sequences may prove to have regulatory significance.