FULL-LENGTH L1 ELEMENTS HAVE ARISEN RECENTLY IN THE SAME 1-KB REGION OF THE GORILLA AND HUMAN GENOMES

New copies of the mammalian retrotransposon L1 arise in the germline a t an undetermined rate. Each new L1 copy appears at a specific evoluti onary time point that can be estimated by phylogenetic analysis. In hu mans, the active L1 sequence L1.2 resides at the genomic locus LRE1. H ere we analyzed the region surrounding the LRE1 locus in humans and go rillas to determine the evolutionary history of the region and to esti mate the age of L1.2. We found that the region was composed of an anci ent L1, L1Hs-Lrg, which was significantly divergent from all other L1 sequences available in the databases. We also determined that L1.2 was absent from the gorilla genome and arose in humans after the divergen ce of gorilla and human Lineages. Ln the gorilla LRE1 region, we disco vered a different full-length L1 element, L1Gg-1, which was allelic an d present at a high gene frequency in gorillas but absent from other p rimates. We determined the nucleotide sequence of L1Gg-1 and found tha t it was 98% identical to L1.2, suggesting a close relationship betwee n active L1s in gorillas and humans.