Fig. 1: Cryo-EM 3D maps of the S. cerevisiae Rad24-RFC–9-1-1–DNA ternary complex.
From: DNA is loaded through the 9-1-1 DNA checkpoint clamp in the opposite direction of the PCNA clamp
a, Domain architecture of the eight proteins of the Rad24-RFC–9-1-1 complex: the clamp loader proteins Rad24 and Rfc2–5 and the 9-1-1 clamp proteins Ddc1, Mec3 and Rad17. The C-terminal collar domain forms the tight pentamer connections. The Rad24 A′ domain is associated with the collar domain that is also present in Rfc1, which Rad24 replaces. The unique Rad24 C-terminal coiled coil (CC) is disordered. The dashed lines indicate unsolved regions. LL is the long linker between the Rad24 AAA+ and collar domains. The red lines between the NTDs and CTDs of the 9-1-1 subunits represent the IDCL between the two domains of each 9-1-1 subunit, and the dashed purple lines represent the long C-terminal tails of Ddc1 and Rad17. b, The DNA substrate used to form the ternary complex. Both a 5′- and 3′-recessed DNA junction are present. Nucleotides in the cyan box are resolved in the structure. c, Segmented 3D maps of the Rad24-RFC–9-1-1 clamp–DNA complex in closed (left) and open (right) states. Maps are surface-rendered at 0.1 threshold, except for Ddc1 in the open conformation, which is separately displayed at 0.07 threshold. d, Model of the closed-state complex in front (left) and back (middle) cartoon view and in a top (N-terminal) surface view (right). e, Sketch comparing the DNA binding mode of the Rad24-RFC–9-1-1 (upper panel, this study) with that of the RFC–PCNA, based on the T4 clamp–clamp loader–DNA structure (lower panel; PDB 3U60). Note the drastically different DNA positions and the spiral versus planar clamp rings of the two systems.
