FIG. 3.

DNA-induced protection against protease digestion of an AidB domain. AidB (50 μg) was digested with 2.5 μg of chymotrypsin for 0, 3, or 6 h in the absence of DNA (lanes 2, 4, and 6) or in the presence of 200 ng of plasmid DNA (lanes 3, 5, and 7) at 37°C. The reactions were quenched with trichloroacetic acid, and the samples were analyzed by SDS-PAGE on an 18% gel. Lane 1 contains molecular mass markers (97.4, 66.2, 45, 31, 21.5, and 14.4 kDa). The band designated by the upper arrow is the 50-kDa fragment that was subjected to Edman degradation, and the band shown by the lower arrow is chymotrypsin.