Prototype of a gene (COL2 A1) for procollagen type II (!1[II])

A procollagen molecule is encoded by a gene
consisting of 52 exons. The translated part of
exon 1 (85 base pairs) codes for a signal peptide
necessary for secretion. Exon sizes differ, with
one exon coding for 5, 6, 11, 12, or 18 periodic
Gly–X–Y units. The genes for procollagen
types I, II, and III differ in that some exons are
fused, but otherwise they are similar, especially
for the three main fibrillar collagen types (I, II,
III).