Comparison of the SiE5′NT structural homology model (green) with the crystal structure of human E5′NT (PDB id 4H2I, red) with 32% sequence identity. C. Comparison of the SiE5′NT structural homology model (green) with the crystal structure of Thermus thermophiles 5′NT (2Z1A, blue) with 36% sequence identity. *: position of the loop involved in dimerization of human E5′NT. 