Fig. 4: Interaction between Rad24-RFC and the 9-1-1 clamp in the closed and open states.
From: DNA is loaded through the 9-1-1 DNA checkpoint clamp in the opposite direction of the PCNA clamp
a, Tilted, bottom and side views of the closed 9-1-1 clamp, highlighting the positions of three important loops. The upper insertion loop of Rad24 and the Rfc5 plug narrow the interior chamber of Rad24-RFC to 12 Å, suitable for ssDNA but excluding dsDNA binding. The Rad24 lower insertion loop binds Ddc1 of the 9-1-1 clamp to control the ring opening/closure. The inner diameter of 9-1-1 is 37 Å. b, Comparison of the closed and open 9-1-1 clamp in top and side surface views. Superimposed on the clamps (in surface view) are the CIH and connecting loop of each loader subunit, shown in cartoon view. The non-canonical PIP (ncPIP) motif and the KYxxL-like motif at the end of the Rad24 CIH are labeled and highlighted in dark red. The Rad24 lower loop bound to Ddc1 is ordered in the closed state but becomes disordered and loses contact with Ddc1 in the open state, leading to a 45° in-plane rotation of Mec3 to form the DNA entry gate.
