 Pyrrolysine-containing genes are known to include monomethylamine methyltransferase (mtmB), dimethylamine methyltransferase (mtbB), and trimethylamine methyltransferase (mttB).Homologs of "pylS" and "pylT" have also been found in an Antarctic archaeon, "Methanosarcina barkeri" and a Gram-positive bacterium, "Desulfitobacterium hafniense".The occurrence in "Desulfitobacterium" is of special interest, because bacteria and archaea are separate domains in the three-domain system by which living things are classified.