Phylogenetic relationship of HTLV-4(1863LE) to other PTLVs in gag using Bayesian inference. First and second codon positions of gag were used to generate PTLV phylogenies by sampling 10,000 trees with a Markov Chain Monte Carlo method under a relaxed clock model, and the maximum clade credibility tree, i.e. the tree with the maximum product of the posterior clade probabilities, was chosen. Branch lengths are proportional to median divergence times in years estimated from the post-burn in trees with the scale at the bottom indicating 100,000 years. Posterior probabilities for each node are indicated. Branches leading to PTLV-1, HTLV-2 and PTLV-3 sequences are drawn in red, blue and green respectively. The branch leading to HTLV-4(1863LE), STLV-2, and to the divergent MarB43 strain are drawn in magenta, purple, and yellow respectively.