Conservation and periodicity of DNA bend sites in eukaryotic genomes.

DNA bend sites appear every 680 bp on average in the human epsilon- and beta-globin gene regions. Although most of their molecular nature has not been unraveled, a potential bend core sequence A2N8A2N8A2 (A/A/A) and its complementary T2N8T2N8T2 (T/T/T) appeared preferentially either in or very close to most of the bend sites, whereas other combinations of A2 and T2 dinucleotides, A/T/T + A/A/T, T/T/A + T/A/A and A/T/A + T/A/T, did not. The distances between any two of the core sequences in the entire beta-globin locus showed a strong bias to a length of 701-800 bp and multiples thereof, suggesting that there is periodicity throughout the locus. This bias was not found for other combinations of A2 and T2. Again, this periodicity was identified in many eukaryotic genes, whereas the tendency was absent in mRNAs and prokaryotic as well as viral genomes.