A, Scheme of HoxA and HoxB. The open reading frame of hoxA is interrupted by one 67 bp long intron (RNAseq data) and encodes a protein of 380 amino acids with a predicted mass of 42.5 kDa. The protein contains a heme binding pocket, a HemeO-like superfamily domain and a C-terminal putative membrane anchor (CTA). In comparison, hoxB is interrupted by a 50 bp intron. The protein (509 amino acids, 55.9 kDa) contains only the HemeO-like superfamily domain. 