FIG. 1.

Unrooted tree of pol sequences from retroviral genomes. Alignment was done using the Clustal-X algorithm. The tree was derived from ungapped portions of the Pol protein alignment. Bootstrap analysis shows that HERV-L and MERV cluster with the foamy viruses 94 of 100 times. The viral designations not given in the text, are as follows: SFV-1 (rhesus macaques), SFV-3 (African green monkey), FFV (feline FV), SHRV (snakehead retrovirus), ALV (avian leukosis virus), MMTV (murine mammary tumor virus), HTLV1 and HTLV2 (human T-cell leukemia virus types 1 and 2), EIAV (equine infectious anemia virus), FIV (feline immunodeficiency virus), SIV (simian immunodeficiency virus type 1). The accession numbers used for endogenous element sequences are: MERV, EMBO no. Y12713, MERVLPOLY; HERV-L, GenBank no. AF070718 and AF070718 (reverse compliment of nucleotides 46480 to 44147, with frameshifts corrected).