Effects of Y25A and Q36R on the catalytic activity of RNase E <i>in vivo</i> and <i>in vitro</i>.

<p>(A) Plasmid copy number of pNRNE4, pNRNE4-Q36R and pNRNE4-Y25A in KSL2000. Plasmids were purified from KSL2000 cells harboring pNRNE4, pNRNE4-Q36R or pNRNE4-Y25A and were digested with <i>Hin</i>dIII, which has a unique cleavage site in all of the plasmids tested. Plasmid copy number was calculated relative to the concurrent presence of the pSC101 derivative (pBAD-RNE), which replicates independently of Rne, by measuring the molar ratio of the ColE1-type plasmid to the pBAD-RNE plasmid. (B) Growth characteristics of KSL2003 cells expressing wild-type N-Rne or the Q36R or Y25A mutant proteins. Growth of KSL2003 cells harboring pLAC-RNE2, pLAC-RNE2-Q36R, or pLAC-RNE2-Y25A was measured individually on LB-agar plates containing 1.0 to 1000 µM IPTG. Numbers on the top indicate the number of bacterial cells in each spot. (C) Plasmid copy number of pET28a in KSL2003. Plasmids were purified from KSL2003, KSL2003-Q36R or KSL2003-Y25A cells harboring pET28a and digested with <i>Hin</i>dIII, which has a unique cleavage site in all the plasmids tested. Plasmid copy number was calculated relative to the concurrent presence of the pSC101 derivative (pLAC-RNE2, pLAC-RNE2-Q36R or pLAC-RNE2-Y25A) by measuring the molar ratio of the ColE1-type plasmid to the pSC101-derived plasmid. (D) Expression profiles of Rne and mutant proteins in KSL2003. The membrane probed with an anti-Rne polyclonal antibody was stripped and reprobed with an anti-S1 polyclonal antibody to provide an internal standard. The relative abundance of protein was quantified by setting the amount of wild-type Rne to 1. KSL2003 cells were grown in LB medium containing 10 µM IPTG. (E) <i>In vitro</i> cleavage of p-BR13 by wild-type N-Rne, Q36R and Y25A mutant proteins. Two pmol of 5′ end-labeled p-BR13 was incubated with 1 pmol of purified wild-type N-Rne or Q36R or Y25A mutant protein in 20 µl of cleavage buffer at 37°C. Samples were removed at each indicated time point and mixed with an equal volume of loading buffer. Samples were denatured at 65°C for 5 min and loaded onto 15% polyacrylamide gel containing 8 M urea. The radioactivity in each band was quantified using a phosphorimager and OptiQuant software.