Dam-mediated adenine methylation at GATC sites can interfere with gene expression. By use of lacZ fusion technology, the efficiency of trpR and trpS promoters (which contain a GATC site) and of trp (the target of TrpR repressor) was analyzed in dam+ and dam- backgrounds. In exponentially growing cells, the dam mutation leads to an increased activity of trpR promoter but does not affect trpS or trp promoters. The Dam-mediated induction of trpR was, however, found to be repressed by trpR-mediated autoregulation. In contrast, trp-lacZ directed beta-galactosidase activity was increased at least sixfold in dam-cells in late logarithmic growth phase. In dam+ cells, expression of trp-lacZ was similarly late-growth-phase induced, albeit to a reduced extent. Hence, we propose that enhancement of growth phase-dependent gene induction constitutes a previously unidentified trait of dam mutation. This finding is discussed in the context of the pleiotropic phenotype of dam mutation.