Fig 9.

T-ag hexamers cannot exist simultaneously on site I and the proximal side of site II. As reported herein, a T-ag hexamer nucleated through the OBDs bound at P5 and P6 positions the helicase domains over the EP region. Furthermore, when T-ag assembles into a double hexamer on site II, the helicase domains span both the AT-rich and EP regions (19). Therefore, if both site I and the EP-proximal side of site II were occupied by T-ag hexamers, the helicase domains would completely overlap and suffer steric clashes.