Sequence alignment of PFV, HIV-1 and Mo-MLV NTD-IN. The secondary structure of Mo-MLV is shown below. α-helices are marked as orange cylinders, and β-strands by blue arrows. Yellow boxes: at least two identical residues, Green boxes: three identical residues. Accession codes: PFV IN, CAA68999; HIV-1 IN, AAC83550 and Mo-MLV IN, P03355.