sequence alignment between "chimeric" H4-H3 histone and the double histone fold (DHF) from Heliothis zea virus 1. Above the alignment, are shown the positions of alpha-helices in histone H4 (green boxes) and histone H3 (yellow boxes). Red letters indicate regions predicted to assume an alpha-helical structure, based on a comparison among the results obtained from three different secondary structure prediction servers (PHD, J-pred, Psi-pred; see Methods). Light blue letters correspond to the basic residues which mediate the contact between the H3-H4 histone dimer and DNA. Underlined residues belong to the pattern of aminoacids whose hydrophobicity is strictly conserved.