Genetic and structural analysis of the essential fission yeast RNA polymerase II CTD phosphatase Fcp1

Fcp1 structure captured as a mimetic of the phosphorane transition state. (Top panel) Stereo view of the active site of Fcp1–BeF₃ complex that mimics the Michaelis complex of the aspartyl-phosphate hydrolysis step. (Bottom panel) Stereo view of the active site of the Fcp1·AlF₃ complex that mimics the transition state of the aspartyl-phosphate hydrolysis step. Selected side chains and main chain atoms are depicted in stick representation. Octahedrally coordinated Mg²⁺ ions are magenta spheres. Waters are red spheres. The fluoride atoms are colored green. The beryllium and aluminum atoms are colored yellow. Atomic contacts are indicated by dashed lines.