Abstract
LINE-1, the major family of long, interspersed repeats in the mammalian genome, moves via an RNA intermediate and encodes its own reverse transcriptase. Comparative sequence analysis was used to reconstruct the phylogenetic history of LINE-1 dynamics in the deer mouse, Peromyscus. As is the case in Mus and Rattus, a very small number of active templates produce the majority of LINE-1 copies in Peromyscus. However, in contrast to the single LINE-1 lineage seen in the muroid rodents, Peromyscus has at least two LINE-1 lineages whose most recent common ancestor probably existed before the peromyscine radiation. Species-specific variants of Lineage 1, and intact open reading frames in the youngest elements of both Lineages 1 and 2, suggest that both lineages have remained active within the same genome. The higher number of shared-sequence variants in Lineage 1 relative to Lineage 2 suggests that Lineage 1 has replaced its master template much more frequently than Lineage 2 or that the reverse transcriptase Lineage 1 is more error prone. The implications of the method used to acquire LINE-1 sequences for analysis are discussed.