A plasmid with the structural uspA gene under the control of a tac promoter was used to study the effects of altering uspA expression levels under various growth conditions. We found that increasing UspA synthesis to levels corresponding to physiologically induced levels decreased the cell growth rate in minimal medium and reduced or abolished the cells' capacity to adapt to upshift conditions. As was demonstrated by two-dimensional gel electrophoresis, increased uspA expression caused global changes in the pattern of protein synthesis. In addition, electrophoretic analysis together with V8 protease peptide mapping demonstrated that the pIs of some specific proteins became more acidic as a result of the elevation of the levels of UspA.