The new transformants were plated on agar plates containing 0, 1.3, 2.6, 3.9, or 5.2 ng/ml of His6-tagged ColE7/ImE7 to confirm their resistance to ColE7. The insert in the plasmid that conferred DH5α resistance to 5.2 ng/ml His6-tagged ColE7/ImE7 was sequenced. A 1,470-bp DNA region on the chromosome at position 3662617 to 3664086 was analyzed that contains both complete gadX and gadY genes. The plasmid was thus named pGadXY (Figure 1). Figure 1 Structures of pGAD10, pGadXY, pGadX, and pGadY. pGAD10 was the vector used to clone gadXY, gadX, and gadY. pGadXY has a 1,470-bp fragment containing gadX, gadY, and a portion of gadW of E. coli K-12 genomic DNA inserted into the EcoRI site of pGAD10. pGadX contains

a DNA fragment carrying the 825-bp gadX also inserted into the EcoRI site of pGAD10. pGadY is derived LY411575 from pGadXY by deleting the 601-bp NcoI-DraIII fragment and

thus contains a truncated gadX, the entire gadY, and a portion of gadW. Nucleotide sequences of the promoter regions Epacadostat nmr of gadX and gadY are shown. The orientation of gadX is opposite to that of gadY. The sigma factor S (RpoS) recognition site and the Shine-Dalgarno (SD) sequence are shown in the 5′ end region of gadX. PADH is the promoter of GAL4-AD and is not functional in E. coli. To determine whether gadX or gadY was responsible for ColE7 resistance, pGadX, pGadY, and pGadXY that contain gadX, gadY, and gadXY, respectively, were separately introduced into E. coli strain DH5α and then assayed for their ability to confer ColE7 resistance. 1 × 105 cells containing pGadX, pGadY, or pGadXY were plated on LB agar containing 1.3, 2.6, 3.9, or 5.2 ng/ml of His6-tagged ColE7/ImE7. Cells containing the vector pGAD10 were also plated to serve as controls. The percent survival of cells containing pGAD10, pGadXY, pGadX, and pGadY in the presence of 1.3 ng/ml of His6-tagged ColE7/ImE7 were 41.7, 95.5, 71.4, and 73.5%, respectively, Dipeptidyl peptidase and 1.5, 63.9, 3.6, and 9.1%, respectively, in the presence of 2.6 ng/ml of His6-tagged ColE7/ImE7. Only pGadXY conferred ColE7 resistance to 3.9 and 5.2 ng/ml of His6-tagged ColE7/ImE7 with 29.1 and 17.1% survival rates, respectively (Table

1). Table 1 Effects of gadXY, gadX, and gadY on ColE7 resistance ColE7 conc./Bacteria pGAD10/DH5α pGadXY/DH5α pGadX/DH5α pGadY/DH5α 1.3 ng/ml 41.7% 95.5% 71.4% 73.5% 2.6 ng/ml 1.5% 63.9% 3.6% 9.1% 3.9 ng/ml 0 29.1% 0 0 5.2 ng/ml 0 17.1% 0 0 Detection of protein whose expression is affected by gadXY To investigate the mechanism by which gadXY affects ColE7 resistance, the expression levels of BtuB, TolQ, TolR, TolA, TolB, Pal, and OmpF that are involved in ColE7 import were determined by Western blotting, and BtuB was the only protein found to be affected. Its expression level was reduced by 93% in the presence of gadXY (Figure 2) as determined by densitometry.