The TF family was characterized by Naas et al.,1998 and DeBerardinis et al., 1998 as a rapidly amplifying family in Mus domesticus containing an F-type promoter array and of nearly identical sequence to two present day full length inserts: L1orl, and L1spa. The sequences AF081104..AF081114 are from the Naas et al. collection. Saxton and Martin, 1998, further characterized the lineage as being a recombinant between an older F-type element from the promoter array through the endo domain in ORF2, and the more modern A2 body for the bulk of ORF2 and the 3' end.
The previously characterized L1Md4 lineage ends in the TF family, and L1Md4 itself is a member of the TF family. For the sake of precision, we use domesticus TF family to mean the burst of output in Mus domesticus, TF lineage to mean all descendants of the ancestral element that experienced the founding recombination, and L1Md4 lineage to mean all descendants of the ancestor that first split away from the A2 lineage. The point of origin of the TF lineage is not known, although Saxton and Martin have shown the presence of TF families in Mus spretus and the sister taxon Mus spicilegus. It is tempting to speculate that the TF recombination occured at the time of the A2/L1Md4 lineage split and somehow drove the split. That would make TF lineage and L1Md4 lineage the same thing. There is, however, another major lineage that splits off the L1Md4 lineage after its inception (Z lineage). The promoter type of the Z lineage is unknown.
The TF lineage exemplifies the burst-like dynamics often observed for LINE-1 subfamilies. The production of several thousand copies has occurred within the last 0.1 Mya. However, in the preceding 0.3-0.5 Mya, there are no copies evident in Mus domesticus. We have conducted targetted cloning experiments aimed at finding such copies, but have recovered none.
The domesticus TF lineage joins the spretus Ms475 & Ms7024 lineages at a time which appears to be after the domesticus/spretus speciation. Therefore, we hypothesize that the spretus Ms475 & Ms7024 lineages are the spretus TF family, and that TF was introduced into M. domesticus by a late transfer. It is not known if the proposed transfer would promote the dramatic burst-like behavior, however the spretus Ms475 & Ms7024 families also exhibit bursts of output (Casavant & Hardies, 1994). In contrast, the lineage in M. spretus is well populated along its length, and M. spretus has about 2x as many total members in its genome.
The domesticus TF family is split into two subgroups by a small patch of differences presumed to be gene conversion from an older element in a narrow segment of the 3' untranslated. The two subgroups are represented by the nodal sequences TFnode1 and TFnode2.
Last update 5/10/99