Sequence characteristics of the gp41 MPER of ITM4 viruses isolated at different time points. The consensus MPER sequence is designated in the first line. The core epitopes of 2F5 and 4E10 are indicated, the key amino acid residues of both epitopes are underlined. MPER sequences derived from a functional Env clone are marked by an asterisk. a Plasma samples used for viral RNA isolation. bYear of sampling. c Number of clones having this motif.