V.A.Engelgardt Molecular Biology Institute RAS (Russia)
Collagen is a fibrous protein of a primary structure with complex periodical features. It plays a vital part in body structure of animals. a most characteristic feature of an amino sequence of collagen is the Gly occupying each third position in collagen sequence. Latter on the so called large periods in collagen were discovered first on electron microscopic and low angle X-ray photographs and later they were identified in the primary structure of the protein. The length of basic period is 234 amino acid residues. This largest period reflects the fundamental periodicity of the molecule and predetermines the molecule aggregation. Many periods - D divisors such as D/13, D/6, D/5 and other were found by different researchers. One of the interesting attempts to explain the origin of collagen periodical structure was the reduplication of a gene precursor. However, little has been done to evaluate the validity of such an idea.
Collagen may serve as a unique object for a study of gene multiplication processes in coding sequences. Indeed, since every third amino acid in collagen protein is Gly, the Gly-coding triplets of the collagen gen does not undergo any selection induced from the protein level. Thus, every third nucleotide in Gly codons depends only on the factors reflecting DNA environment and gene history.
We show using symbolic Fourier transform of the collagen cDNA sequence that basic periodical patterns appear also in DNA sequence. Strikingly they are present in third position of triplets coding Gly, which occupies each third position in the sequence of the protein, and to which selection on the protein level does not applied. thus, the gene of collagen seems to appear due to pra-gene multiplication.