Human UCKL-1 (UniprotKB Q9NWZ5), UCK1 (Q9HA47) and UCK2 (Q9BZX2) were aligned using the Clustal program. Identical amino acids among the three proteins are highlighted in yellow. Similar amino acids between UCKL1 and either UCK1 or UCK2 are depicted in red. The boxed amino acids represent the ATP binding site. The section of UCKL-1 highlighted in blue has 41% similarity to human UPRT (Q96BW1).