Figure. Xenotropic murine leukemia virus–related gammaretrovirus (XMRV) gag sequences derived from respiratory tract secretions. Phylogenetic tree comparing the 390-nt gag fragment of all respiratory samples of this study with recently published XMRV sequences from patients with familial prostate cancer (1). The edited sequences were aligned with ClustalX version 1.82 (13,14) by using default settings. The tree was generated on the basis of positions without gaps only. Sequences are labeled as X, xenotropic; P, polytropic; mP, modified polytropic; S, sputum, IS, immunosuppression; TS, tracheal secretion; and C, control. Scale bar indicates nucleotide substitutions per position.