Phylogenetic relationships of mysTR to known retrovirus genera, both endogenous and exogenous. Unrooted maximum likelihood trees are based on nucleotide sequences of reverse transcriptase domains 1 to 4 (42). Posterior probabilities or bootstrap values are noted on select branches. Panel A contains four mysTR elements from each species included in the study, representative elements of betaretrovirus subgroups β1 to β7 (3), the endogenous betaretrovirus HERV-K10, and RSV (an alpharetrovirus). Panel B contains two representatives each of mysTR and the retrovirus genera Alpharetrovirus (α), Betaretrovirus (β), Deltaretrovirus (δ), Epsilonretrovirus (ε), Gammaretrovirus (γ), Lentivirus, and Spuma-like virus plus HERV-K10.