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9.B.344.  The Uncharacterized Archaeal 4 TMS Protein (UA4P) Family 

The proteins of the UA4P family are usually about 200 aas in length and have 4 TMSs often in a 1 +2 + 1 TMS arrangement.  They are found exclusively in archaea, mostly in Lokiarchaeota and Methanomassiliicoccus species.  In the latter organisms, there are both 4 and 8 TMS proteins.  In the latter, the two halves are both homologous to the 4 TMS proteins.  This provides evidence that these proteins may be transporters that function as homodimers of two 4 TMS proteins or as monomers of the 8 TMS proteins.