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. 2011 Dec 23;40(8):3316–3328. doi: 10.1093/nar/gkr1247

Figure 5.

Figure 5.

StpA protein filament was able to block DNA access. (A) Normalized DNA tethers as a function of time with a tether population of 8–10. Adding 320 nM DNase I in 50 mM KCl (Black line) caused all the DNA tethers (total eight DNA tethers) to be cleaved by 30 s. Adding 600 nM StpA and then 320 nM DNase I in the same buffer condition (red line) resulted in loss of only one DNA tethers after 4 min (total eight DNA tethers). Thus, StpA protein filament protects DNA from DNase I digestion. (B) In 500 mM KCl where StpA does not form a protein filament. 320 nM DNase I in 500 mM KCl showed minimal digestion activity on naked DNA (black line). To improve the digestion efficiency, we used four times more DNase I (1280 nM) which could cut all the naked DNA tethers (total 10 DNA tethers) by 180 s (red line). Adding 600 nM StpA and then 1280 nM DNase I in 500 mM KCl, all the DNA tethers (total eight DNA tethers) were cut by 120 s (green line). Thus, the absence of filament formation in 500 mM KCl does not protect DNA from being digested.