Methanosarcinaceae

[1] The currently accepted taxonomy is based on the List of Prokaryotic names with Standing in Nomenclature (LPSN)[2] and National Center for Biotechnology Information (NCBI)[1] Methanohalobium Zhilina & Zavarzin 1988 Methanosalsum Boone and Baker 2002 Methanococcoides Sowers and Ferry 1985 Methanohalophilus Paterek and Smith 1988 Methanomethylovorans Lomans et al. 2004 Methanolobus König and Stetter 1983 Methanimicrococcus Sprenger et al. 2000 Methanosarcina Kluyver and van Niel 1936 Methanimicrococcus Methanosarcina Methanohalobium Methanosalsum Methanococcoides Methanohalophilus Methanomethylovorans Methanolobus A notable trait of Methanosarcinaceae is that they are methanogens that incorporate the unusual amino acid pyrrolysine into their enzymes.

The unusual amino acid is inserted using a unique tRNA, the anticodon of which is UAG.

In most organisms, and in most Methanosarcinaceae proteins, UAG is a stop codon.

However in this enzyme, and anywhere else pyrrolysine is incorporated, likely through contextual markers on the mRNA, the pyrrolysine-loaded tRNA is inserted instead of the release factor.

They also have a unique aminoacyl-tRNA synthetase to specifically load this tRNA with pyrrolysine.