Helix I in the alphavirus CP. (A) Sequence alignment of amino acid residues in helix I from indicated alphaviruses. Letters above the alignment identify amino acid positions in a coiled coil helix. Invariant residues are marked by asterisks; residues that are identical to the SINV amino acids are represented by dashes. (B) Coiled coil representation of helix I of SINV. The invariant leucine residues exclusively occupy the d position of the helix, and β-branched residues occupy the a position. Abbreviations (NCBI protein numbers): SINV (130579), Sindbis virus; AURAV (4240569), Aura virus; EEEV (130557), eastern equine encephalitis virus; WEEV (130581), western equine encephalitis virus; VEEV (130559), Venezuelan equine encephalitis; SPDV (4808420), salmon pancreatic disease virus; RRV (130571), Ross River virus; SFV (130577), Semliki Forest virus; CHIKV (576465), Chikungunya virus; ONNV (130568), O'nyong-nyong virus. Numbering corresponds to amino acid residues of the SINV CP.