FIG. 2.

Ability of untreated and tBHP-oxidized α/β-type SASP to provide DNase protection to plasmid pUC19. Purified SspC and SASP-C were treated with tBHP for 3 h, dialyzed, complexed with linearized plasmid pCU19 DNA, and DNase treated as described in Materials and Methods. DNA was isolated and analyzed by agarose gel electrophoresis. The arrows labeled a and b indicate the positions of 2.3- and 0.56-kb DNA size markers, respectively. Samples run in the various lanes are as follows: lane 1, SspC without DNase treatment; lane 2, no α/β-type SASP; lane 3, untreated SspC; lane 4, tBHP-treated SspC; lane 5, untreated SASP-C; and lane 6, tBHP-treated SASP-C. SspC contained ∼3 and ∼21% methionine sulfoxide at M27 and M67, respectively. Oxidized SspC contained ∼79 and ∼86% methionine sulfoxide at M27 and M67, respectively. SASP-C and oxidized SASP-C contained ∼8 and ∼88% methionine sulfoxide at M28, respectively. Oxidized SspC and SASP-C also showed ∼8 and ∼17% oxidation at lysines 28 and 29, respectively. The bands at ∼2.7 kb in lanes 3 and 6 are probably microdrops of the incubation mixtures which escaped exposure to DNase.