Figure 1.

Analysis of TraB_s ATPase activity. A, schematic representation of Streptomyces TraB of plasmid pSVH1. Black bars represent the N-terminal transmembrane helices, as predicted with TMHMM (www.cbs.dtu.dk/services/TMHMM-2.0).⁴ The motor domain is depicted in gray and the C-terminal γ-domain in gray squares. TraB_s consists of a deletion of the first 270 residues that contain the transmembrane helices, whereas TraB_sΔγ also contains a deletion of the C-terminal γ-domain. B, pH-dependence of TraB_s ATPase activity. ATP turnover was measured using a coupled spectrophotometric assay. Reactions contained TraB_s (50 nm), 5 mm ATP, and 45 bp dsDNA (250 nm), buffered at the corresponding pH value. C, effect of ssDNA and dsDNA on TraB_s ATPase activity. Reactions were carried out at increasing concentrations of ssDNA or dsDNA substrates, represented as micromolar concentrations of bases (for ssDNA) or bp (for dsDNA). Black triangles, TraB_s + dsDNA, formed by the annealing of 45-mer nucleotides A and B; black dots, TraB_s + ssDNA (oligonucleotide A). Data were fit to a Hill equation and represent the average of at least three different experiments. Error bars: S.D.