Figure 4. The agrA mRNA level is increased and stabilized in the cshA mutant strain. (A) RNA was isolated from exponentially growing cultures (approx. OD₆₀₀ = 0.4) of the S30 wildtype and the cshA mutant. qRT-PCR was performed to determine the level of agr mRNA, using the HU mRNA as an internal reference. An unpaired T-test was performed to show that the difference in agr levels was significant (p = 0.0016). Error bars show the standard deviation. (B) Cultures of S30 (gray squares) and the cshA mutant (black diamonds) were rifampicin treated to block de novo RNA synthesis. Samples were taken for RNA isolation at 0, 2.5, 5, 15 and 30 min after treatment, and qRT-PCR was performed using primers and probe specific for agrA, and using HU mRNA as an internal reference. The quantity of agr, relative to HU, was normalized to 100% at time zero, and plotted in the graph. Error bars represent the 99% confidence level. The figure shows a single experiment out of three biological replicates.