Multiple sequence alignment of all C-5(6) sterol desaturases using the Clustal X program with default parameters. The sequences displayed belong to Leptosphaeria maculans (Lm; accession number AAN27998), Saccharomyces cerevisiae (Sc; NP_013157), Homo sapiens (Hs; NP_008849), Mus musculus (Mm; NP_766357), Arabidopsis thaliana (At; NP_186907), and Tetrahymena thermophila (Tt; XP_001029976). Histidine clusters (I, II, and III) are indicated with black lines, and predicted transmembrane regions are indicated with cross-hatched rectangles. The conserved hydroxylated amino acid is marked with an arrow, and highly conserved domains are marked with a dotted line. Identical amino acid columns are shown in dark gray; conserved substitutions are shown in light gray.