Copy number of the chicken type II procollagen gene.

The copy number of the type II procollagen gene has been determined by quantitative hybridization of cloned DNA to Southern blots of total cellular DNA from chicken. Two different DNA probes have been used. One contains the 289 base pair exon coding for the junction between the triple helical domain and the carboxyl-terminal propeptide and the other contains an 162 base pair exon coding for amino acids 712-765 of the triple helical domain. Both fragments hybridize to single bands present at one copy per haploid genome in genomic DNA from chicken liver or sternal cartilage after these DNAs are cleaved with either HinfI of PstI. When the hybridization stringency and washing conditions were modified sufficiently to stabilize hybridization of heteroduplexes with up to 31% mismatch, no additional hybridizing fragments were detected. These results show that there is not a second copy of this gene or a pseudogene which is more closely related to the type II procollagen gene than the alpha 1 type I procollagen gene. These studies suggest that the cartilage 3 alpha collagen chain, which appears to be very similar to the alpha 1 (II) collagen chain, is encoded by the type II procollagen gene but is differently processed than the major type II gene product, and that the alpha 1 (II) Minor chain identified in bovine type II collagen preparations most likely represents an allelic form of type II collagen rather than a product of a different gene.