Figure 4.

Effects of growth phase and σ^S on sodCI and sodCII expression. Expression of both P_sodC1-lacZ and P_sodCII-lacZ fusions increases during the transition from exponential growth to stationary phase. However, expression of P_sodC1-lacZ is σ^S-independent and subsequently declines, whereas σ^S -dependent expression of P_sodCII-lacZ is sustained. β-Galactosidase activity in Miller units (32) from S. typhimurium 14028s (wild-type) or SF1005 (rpoS) carrying P_sodC1-lacZ or P_sodCII-lacZ fusions is shown in A. The OD₆₀₀ of S. typhimurium 14028s carrying P_sodC1-lacZ is shown in B; growth curves were highly similar for all strains tested.