Jule from the fish Xiphophorus is the first complete vertebrate Ty3/Gypsy retrotransposon from the Mag family

Jule is the second complete long-terminal-repeat (LTR) Ty3/Gypsy retrotrans poson identified to date in vertebrates. Jule, first isolated from the poec iliid fish;Xiphophorus maculatus, is 4.8 kb in length, is flanked by two 20 2-bp LTRs, and encodes Gag (structural core protein) and Pol (protease, rev erse transcriptase, RNase H, and integrase, in that order) but no envelope. There are three to four copies of Jule per haploid genome in X. maculatus. Two of them are located in a subtelomeric region of the sex chromosomes, w here they are associated with the Xmrk receptor tyrosine kinase genes, of w hich oncogenic versions are responsible for the formation of hereditary mel anoma in Xiphophorus. One almost intact copy of Jule was found in the first intron of the X-chromosomal allele of the Xmrk proto-oncogene, and a secon d, more corrupted copy is present only 56 nt downstream of the polyadenylat ion signal of the Xmrk oncogene. Jule-related elements were detected by Sou thern blot hybridization with less than 10 copies per haploid genome in num erous other poeciliids, as well as in more divergent fishes, including the medakafish Oryzias latipes and the tilapia Oreochromis niloticus. Database searches also identified Jule-related sequences in the zebrafish Danio reri o and in both genome project pufferfishes, Fugu rubripes and Tetraodon nigr oviridis. Phylogenetic analysis revealed that Jule is the first member of t he Mag family of Ty3/Gypsy retrotransposons described to date in vertebrate s. This family includes the silkworm Mag and sea urchin SURL retrotransposo ns, as well as sequences from the nematode Caenorhabditis elegans. Addition al related elements were identified in the genomes of the malaria mosquito Anopheles gambiae and the nematode Ascaris lumbricoides. Phylogeny of Mag-r elated elements suggested that the Mag family of retrotransposons is polyph yletic and is constituted of several ancient lineages that diverged before their host genomes more than 600 MYA.