Structure of Utp23 PIN domain. (A) Ribbon representation of the domain-swapped dimer. Two molecules are shown in green and magenta. (B) The 2fo-fc electron density contoured at the 1.5 σ level is overlaid on the refined structure. (C) Monomeric structure model of Utp23 PIN domain. Two orthogonal views are shown. The β-strands, α-helices, and loops are colored in yellow, red, and green, respectively. The zinc ion is shown as a yellow ball. The secondary structures and the N and C termini are labeled. (D) Topology diagram of the Utp23 PIN domain. The secondary structures that are common to other PIN domains are colored green for α-helices and yellow for β-strands, and those unique to Utp23 are shown as empty boxes. Four zinc-coordinating residues are labeled. (E) Close-up view of the zinc-finger motif. (F) Structural superimposition of Utp23 (green) and SMG6 (PDB code 2HWW, gray). The catalytic residues of SMG6 and their Utp23 equivalents are shown as sticks. Utp23 residues are labeled.
