The E. coli ΔselA strain JS1 was complemented with E. coli selA (lane 1), empty vector control (lane 2), M. jannaschii spcS (coding for SepSecS, lane 3), M. jannaschii pscS (coding for SepCysS, lane 4), M. jannaschii spcS and pstK genes (lane 5), and M. jannaschii pscS and pstK (lane 6). Two major bands were observed in the positive control lane 1. Based on the molecular weight marker, the upper band corresponds to FDHH. The lower band is likely a degradation product of FDHH, the sole selenoprotein in E. coli in the indicated growth conditions.