Fig. 4

Identification of the amino acid responsible for the loss of functionality in R1 chimeras. a Sequence alignment between regions R1 of the Env B and G showing the four amino acids differing between the two sequences: positions 198, 200, 201 and 202 (numbering according to HxB2). Color code is the same as for Fig. 2a. b Left Schematic representation of the B C2G chimeras carrying the substitutions of the individual amino acids indicated. Color code: Env B grey, Env G black. Right Functionality of the Env depicted on the left. The functionality of B C2G is given as reference on the left of the dotted line. n varies between 4 and 9, according to the sample considered. c Sequence logo (WebLogo, http://weblogo.berkeley.edu/logo.cgi) for R1 sub-regions of different subtypes are shown, subtype A at top left, subtype B top right, subtype C bottom left and subtype G bottom right; the relative prevalence at the position equivalent to position 202 is indicated. The sequence of the isolates used in our study is given on the top of each sequence logo. Color code: purple weakly basic residues, green polar residues, black hydrophobic residues, blue basic residues. d Schematic representation (left) and level of functionality (right) of Env B 202G and of Env G 202B. Percentages of functionality were calculated as for Fig. 1. n varies between 6 and 9, depending on the sample considered