Fig. 6.

Unrooted phylogenetic trees of representative retroviruses (Additional file 9: Table S2) based on a MUSCLE multiple alignment and neighbor-joining method. Asterisks indicate bootstrap values greater than 70. Horizontal branch lengths are proportional to the degree of amino acid substitutions per site. The three trees represent RTpol (A), the MHR region of CAgag (B) and a segment of TMenv (C). The RT tree identifies the clusters representative of the seven RV genera. The arrowheads in the TMenv tree identify sequences with the N-linked glycosylation site associated with a heptad “stutter” (Additional file 7: Fig. S7)