Fig. 3: Four ATPγS and one ADP are bound to Rad24-RFC.
From: DNA is loaded through the 9-1-1 DNA checkpoint clamp in the opposite direction of the PCNA clamp
a, Key ATPase motifs in Rfc2–5. Rad24 lacks the SRC and central helix. b, Top view of Rad24-RFC–DNA in cartoon, omitting the 9-1-1 clamp for clarity. The bound four ATPγSs and one ADP are shown as sticks. c–e, Enlarged views of the nucleotide binding pockets in Rad24 (c), Rfc4 (d) and Rfc5 (e). ATPγS binding in Rfc2 and Rfc3 is similar to that in Rfc4 and Rfc3 and is not shown. The residues of the AAA+ module involved in nucleotide binding are the conserved SRC (serine-arginine-cysteine) motif, sensor-1, Walker A (P-loop), Walker B (DExx box), Sensor-2 and the central helix; these are labeled and colored red, orange, yellow, cyan, blue and purple, respectively. The Mg2+ ion is in green. The Rfc5 nucleotide pocket is occupied by ADP. Because Rad24 lacks the SRC motif, there is only one arginine (Arg-478) at the Rfc5:Rad24 interface, which points away from the nucleotide due to the absence of the γ-phosphate. The isolated strong density (displayed at 6σ) next to ADP is modeled as a thiophosphate (SPi) and is shown in gray sticks. The phosphate is coordinated by both Lys-49 and Lys-50 of the Walker A motif as well as the backbone nitrogen of Glu-142 in the Walker B motif. For clarity, only the hydrogen bonds with the nucleotide phosphates are shown.
