Northern blots for A) the 5S RNA level in SL1344 and B) sYJ20 level in SL1344 and the Δ hfq strain (JVS-0255) in the presence of ciprofloxacin. A) Lane 1 and 3 (also labelled as -) were loaded with SL1344 total RNA extracted from cells grown under normal conditions (RDM, shaking, 37°C); lane 2 was loaded with SL1344 total RNA extracted from cells challenged with half the MIC of tigecycline (0.125 μg/ml); lane 4 was loaded with SL1344 total RNFA extracted from cells challenged with half the MIC of tetracycline (1 μg/ml). All lanes were loaded with 125 ng of total RNA. The experiment was repeated 4 times. Densitometric analysis of the results showed little or no difference in 5S RNA expression level in the three growing conditions (5Stigecycline: 5Scontrol = 0.88, 5Stetracycline : 5Scontrol = 1.15, average of 4 different experiments). B) Both strains (SL1344 and the hfq deletion strain (JVS-0255, Table2)) were challenged with sub-inhibitory concentration of ciprofloxacin (0.0078 μg/ml) before the total RNA was extracted and probed for sYJ20 by northern blot. As shown above, the Δhfq strain (right lane) produced less sYJ20 compared to SL1344 (left lane). 5S RNA was used as a loading control.