FIG. 3.
DNA helicase activity of TraI and TraIΔ252. DNA unwinding assays using a 93-bp partial duplex substrate (A) or an 851-bp partial duplex substrate (B) were performed as described in Materials and Methods, using the indicated amount of TraI (•) or TraIΔ252 (○). Reaction mixtures were incubated for 10 min at 37°C, and the products were resolved on a native polyacrylamide gel. The fraction of the substrate unwound was calculated by the formula [(U − Bu)/(S − Bs + U − Bu)] × 100, where U represents the DNA in the product band, S represents DNA in the substrate band and Bu and Bs represent background levels of DNA at the position of the product (Bu) or the substrate (Bs) determined from reaction mixtures containing no protein that were either incubated as described above or incubated at 95°C for 5 min to denature the substrate.