An archaeal S-layer gene homolog with repetitive subunits.

An S-layer protein gene homolog of the slgA gene of two Methanothermus species was found in the genome of another methanogenic archaeon of a different family, Methanosarcina mazei S-6. The new gene (slgB) encodes a molecule (SlpB) with the characteristics of S-layer proteins. The N-terminal half of SlpB is 44% identical to that encoded by SlgA, but the other half shows distinctive features: four 56 amino acid long tandem repeats, and Trp-Xaa-Trp clusters located six amino acids from the N-terminus of each repeat.