Figure 3.
IraP, but not IraPL9S, overcomes RssB overexpression. (A) The half-life of σS was measured in exponentially growing cells at 37°C in LB after 15 min of induction with 1 mM IPTG. Protein synthesis was inhibited with tetracycline at an OD600 of ∼0.3, and samples were removed at specific time points and analyzed by immunoblot with an anti-σS antiserum. The strain AB011 (rssA2∷cm background) containing the vector control pQE-80L, pQE-IraP-His6, or pQE-IraPL9S-His6 was used. In the absence of IPTG, σS was not detected with any of the plasmids listed above (data not shown). The levels of His-tagged IraP protein expressed were analyzed by immunoblot using an anti-RGS-His4 antibody. RssB levels were determined by immunoblot with anti-RssB antiserum. (B) Quantification of the levels of σS in panel A. σS half-lives (t½) were determined from plots of the log of intensity versus time.