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9.B.109 The Putative Archaeal 2 TMS Holin (A2-Hol) Family

The archaeon, Candidatus Nitrosoarchaeum limnia, encodes adjacent genes designated Toxin Secretion/Lysis Holin.  The 'toxin' gene encodes a soluble protein of 325 aas stated as belonging to the 'Glycosyltransferase GBT-type Superfamily'.  This protein brings up other glycosyltransferases in NCBI BLAST searches. The adjacent gene encodes as small protein of 132 aas and 2 TMSs that could be a holin, based on its size and topology, but it could also be a 2 TMS counterpart to the other 2 TMS protein of a two-comoponent transport system. This is suggested because several members of the family have 4 TMSs instead of 2 TMSs.  The first protein has the UniProt accession number of S2E3C4 and has been assigned TC# 9.B.109.1.1.  Paralogues are found in this same organism and other closely related species. This TC family (9.B.109) appears to be related to TC family 9.B.116 which shows significant sequence similarity with members of 9.B.109 and has the same topology with members having either 2 or 4 TMSs.