The third nucleotide of the Gly coding triplet remembers the periodicity of the collagen chain.

Collagen is a fibrous protein with a primary structure with complex periodical features. We show using symbolic Fourier transform of the collagen cDNA sequence that basic periodical patterns appear there also. Strikingly they are present in the third position of triplets encoding 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.