FIG. 1.
A nutritional upshift leads to rapid induction of T4S genes. TraM protein and traA mRNA levels as well as DNA transfer frequencies were determined in different phases of bacterial growth. Analyses were performed in stationary phase as well as at the indicated time points after providing E. coli MG1655 cells harboring plasmid R1-16 with fresh media. (A) Analysis of the 14-kDa TraM protein by Western blotting. A part of the Coomassie-stained SDS gel with a 40-kDa protein is shown to demonstrate equal loading. (B) Northern blot analysis of traA mRNA levels. 23S rRNA is shown as a loading control. (C) Mating assays. The transfer frequencies (filled diamonds) and culture densities (OD600; open circles) are shown. Values represent means of results from three independent experiments. No error bar indicates that the standard deviation was below the graphical resolution of the drawing program. Numbers on the x axis indicate minutes after dilution of the cultures into fresh medium. S, stationary phase.