The Gene Coding for Tropoelastin is Represented as a Single Copy Sequence in the Haploid Sheep Genome

The identity of the primary in vitro translation products of fetal sheep nuchal ligament elastin mRNA was confirmed as two distinct polypeptides of 63 Kdal and 65Kdal in both rabbit reticulocyte and wheat germ extract cell-free translation systems. Both polypeptides were co-translationally processed by a microsomal membrane signal peptidase, with the removal of 20–25 amino acid residues. A single (3.5 kb) RNA species encodes both tropoelastin polypeptides. Restriction endonuclease mapping of sheep genomic DNA by hybridisation with two radiolabelled genomic DNA fragments containing sequences coding for sheep tropoelastin (pSE1-1.3 and pSE1-0.7,) indicated the presence of a single elastin gene. The elastin gene copy number was further quantitated by comparison of hybridisation of pSE1-1.3 and pSE1-0.7 to slot-blots and Southern transfers of sheep genomic DNA and to standard curves constructed with each clone. These results clearly demonstrate that each of these sequences is represented only once per haploid genome, suggesting that the two tropoelastin polypeptides are products of a single elastin gene.