Fig. 3. Amino acid alignment of NOA and its closest vertebrate relative ELOVL6. (Hs, Homo sapiens; Mm, Mus musculus; Dr, Danio rerio). Identical amino acids are shown on a black background, similar amino acids/conservative changes on grey background. The position of the transmembrane domains (Hofmann and Stoffel, 1993), which are common to all ELO proteins, is indicated by dashed lines above the sequences for the mammalian homologues and below the sequences for NOA. The conserved histidine motif HXXHH in the centre of the protein (aa 147-151) is indicated. It is a Fe-chelating ligand used for electron transfer in O₂-dependent redox reactions (Shanklin et al., 1994). A putative ER localization signal is found at the C terminus (di-lysine motif) (Gaynor et al., 1994; Schröder et al., 1995). Two potential N-glycosylation signals (NYS and NWT) at the N terminus suggest, that the N terminus resides in the ER and the C terminus on the cytoplasmic side as proposed for other ELO proteins (Tvrdik et al., 2000).