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| Description: DNA gyrase of E. coli; the example shown is a tetrameric protein with two A and two B subunits. The enzyme is shown introducing two negative turns and changing the linking number from +1 to -1. The enzyme catalyzes a double-strand break, and the two DNA ends are bound by A subunits, which move the DNA ends apart so that the unbroken duplex can pass through the gap. Resealing converts the positive supertwist to a negative one, giving the overall molecule a DL of -2. Type II topoisomerases can relax underwound duplexes by the reverse of the above pathway. Picture Stats: Views: 262 Filesize: 55.07kB Height: 265 Width: 270 Source: https://biology-forums.com/index.php?action=gallery;sa=view;id=34960 |