Abstract
Among a variety of putative transposable elements found in the liverwort Y chromosome, one class contains a DNA methyltransferase (DNMT) domain associated with the polyprotein typical for retrotransposons, and was designated as DNMT-containing repetitive element (DRE). To date, no retrotransposon associated with DNA methyltransferase has been reported. DRE has gag-pol genes of Ty3-gypsy type and long terminal repeats (LTRs), but the 3'-LTR is located between another pair of direct repeat. The DNMT domain shows the highest similarity to that of the mammalian DNA methyltransferase 3A (DNMT3a), which is required for imprinting of germ cells. Furthermore, each copy of DRE appears to have incorporated a reverse-transcribed product of different mRNA. Approximately 150 copies of DRE are present in both the male and female genomes, but the mechanism of its transposition is currently unclear.
