2.1.1.98 hanging-drop vapour-diffusion method at 20°C, structure is resolved at 2.0 A resolution. The homodimeric crystal structures of the archaeal diphthine synthases from Pyrococcus horikoshii DSM 12428 and Aeropyrum pernix DSM 11879 share the same overall fold as the cobalt-precorrin-4 methyltransferase CbiF 2.1.1.98 microbatch method, structure is resolved at 2.1 A resolution. The homodimeric crystal structures of the archaeal diphthine synthases from Pyrococcus horikoshii DSM 12428 and Aeropyrum pernix DSM 11879share the same overall fold as the cobalt-precorrin-4 methyltransferase CbiF