Fig. 3

Schematic illustration of sequence length variation, primer target site of two frequently used primer sets F1aCu-R3Cu [33] and nirK1F-nirK5R [34], and different types of indels and extensions observed in 267 NirK sequences. The 375 aa long sequence of Rhodobacter sphaeroides ATCC 17025 (pdb accession number 1ZV2) was used as reference. Size and, if possible, information on taxon or clade defined by these indels or extensions are represented. Copper binding sites, essential active site residues and conserved regions are indicated in red, blue and green respectively. The copper binding His included in the reverse primer target sites is underlined. Abbreviations of copper binding and active site residues are presented due to limited space, with H: His, C: Cys, D:Asp and M:Met