Foldability and the amino acid compositions of exons and introns

Various procedures are employed to relate the structural tendencies of polypeptide chain fragments to amino acid residues that in general have low background frequencies. A numerical evaluation of the content of these amino acids, named amino acid diversity, is defined. Distributions of the amino acid diversity parameter in databases containing exons, introns, and randomized exons show that there is a small difference between exons and shuffled exons, a detectable difference between exons and introns, and a large difference between exons and totally randomized exons.