Methionine sulfoxide reduction in ciliates: Characterization of the ready-to-use methionine sulfoxide-R-reductase genes in Euplotes

► Two msrB genes were cloned from one polar and one temperate-water Euplotes species. ► Both lack canonical structural information for the transcription regulation. ► Both are constitutively expressed and behave as housekeeping genes. ► One of the 2 expressed proteins includes a 7th Cys in addition to the canonical 6. ► The second protein includes cold-adaptive amino acid substitutions.