Triple screws were, however, generally larger and heavier than the twin-screw arrangements preferred by most other navies.
(2) The open PCNARFCATP complex binds to a P/T junction and (3) adopts the notched screw cap arrangement.
Furthermore, the DNA footprints could only be mapped in the presence ATPγS, demonstrating that the notched screw cap arrangement occurs prior to ATP hydrolysis within the RFC ATPase sites.
After adopting the notched screw cap arrangement, the RFCATPPCNAP/T DNA complex undergoes a second conformational change (kdec,1) which requires ATP hydrolysis.
Once formed, the open clampclamp loader complex binds a P/T junction, adopting a 'notched screw cap arrangement' that matches the helical geometry of the DNA duplex (Simonetta et al., 2009; Kelch et al., 2011).
In the notched screw cap arrangement, the ATPase sites of clamp loaders are aligned properly for catalysis and ATP hydrolysis is optimized (Simonetta et al., 2009; Kelch et al., 2011).
Together, this suggests that kinc represents the RFCATPPCNA complex adopting the notched screw cap arrangement on P/T DNA (step 3) in which all RFC ATPase sites are occupied by ATP.
Although the structure of such complexes have yet to be determined for the human system, the asymmetric DNA footprints of human RFC alone and the RFCPCNA complex exactly agree with that predicted by crystal structures of the notched screw cap arrangement from other organisms (Tsurimoto and Stillman, 1991; Bowman et al., 2004; Kelch et al., 2011).
The selection of the stand-off screw size and arrangement was based on the results of the composite beams study described in the previous section.
