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. 2007 Aug 17;93(11):3783–3797. doi: 10.1529/biophysj.107.109546

FIGURE 1.

FIGURE 1

Sketch of PcrA helicase translocating 3′ to 5′ along ssDNA. Shown on the left is a PcrA-DNA complex with PcrA shown in surface representation and DNA in cartoon representation. The ATP binding site (ATP shown enlarged) is highlighted. PcrA domains 1A, 2A, 1B, and 2B are colored green, red, yellow, and blue, respectively. Shown in the middle is a sketch of the helicase on the ssDNA near a junction formed by dsDNA and ssDNA. The directed translocation is powered by ATP hydrolysis. Shown on the right is a rudimentary physical model explaining the directed translocation (11,13): PcrA is represented through two of its domains, 1A and 2A (green and red), in the state without ATP/ADP bound (product state (top and bottom)) and with ATP bound (substrate state (middle)). As suggested in (8,11), unidirectional translocation comes about through alternating domain mobilities along ssDNA controlled by energy barriers.