Figure 1.

Expression of aqpZ in E. coli. (A) Northern analysis of total RNA (25 μg) extracted from E. coli MC4100 cells in the logarithmic phase of growth and hybridized with a ³²P-labeled aqpZ coding sequence (see Materials and Methods). A single 0.7-kb signal was observed (arrow). (B) Expression of aqpZ during growth. E. coli DH5α cells transformed with pANG532 bearing the aqpZ∷lacZ fusion gene, were evaluated for β-gal activity during growth in M9 medium (240 mosM) and assessed by OD₅₇₈ (see Materials and Methods). Shown are the mean and standard error for four separate experiments. (C) Effect of the steady-state extracellular osmolality on the transcription rate of aqpZ. E. coli DH5α cells transformed with pANG532 when grown in M9 media made hypotonic (80 mosmol/kg H₂O) by dilution with water or made hypertonic (700, 1160, and 1530 mosmol/kg H₂O) by adding NaCl. β-Gal activities were measured at the mid-logarithmic growth (OD₅₇₈ = 0.7) and normalized to the number of cfu. Solid columns represent aqpZ∷lacZ expression. Stippled columns represent GM37, an E. coli strain carrying a single proU∷lacZ hybrid gene inserted into its chromosome, studied in parallel as a positive control for hyperosmolar induction. Shown are the mean and standard error for three to five separate experiments.