Extended Data Fig. 8: Conservation of DNA melting mechanisms between LTag and CMG helicases.

This figure highlights the internal DNA separation mechanism within the LTag helicase bound to forked DNA and its resemblance to the yeast CMG double hexamer structure during DNA melting at the origin⁵¹ (dCMGE; PDB 7z13). In both cases, the formation of a separation wedge is facilitated by ATP binding, the staircase arrangement of DNA binding loops, and the engagement of these loops with the tracking strand. These elements collectively drive strand separation within the helicase inner chamber, positioning the helicase for ATP-powered translocation. This configuration is mirrored in the translocating CMG structure⁴⁶ (PDB 6u0m), showcasing the conserved mechanism of action. Conversely, the pre-CMG formation MCM double hexamer⁵⁰ (dMCM; PDB 7p30) displays planar DNA binding loops and a disengaged tracking strand, indicative of a state not yet primed for ATP-dependent movement.