Sequence logo and interaction models for theS-helix. A) The sequence logo generated using the Weblogo program  is shown. The 'a' and 'd' positions of each of the 5 heptads, as per the notation of MacLachlan and Stewart , is also shown below the logo. B) the heptad interaction between two parallel helices is shown. The dotted red arrow indicates the 'g'-'e' interaction. The red negative sign ("-") indicates that most prevalent residues at the b and c positions are negatively charged. C) The most prevalent residue of each position on the S-Helix is shown as a table with the rows showing the positions in each heptad, and the columns showing the five heptads. The residues in red indicate the highly conserved positions.