, Volume 23, Issue 1, pp 21-25

Evidences against a role for adenine methylation in the tryptophan biosynthetic pathway inEscherichia coli and for a growth phase-dependent induction of thetrp promoter

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Abstract

Dam-mediated adenine methylation at GATC sites can interfere with gene expression. By use oflacZ fusion technology, the efficiency oftrpR andtrpS promoters (which contain a GATC site) and oftrp (the target of TrpR repressor) was analyzed indam + anddam backgrounds. In exponentially growing cells, thedam mutation leads to an increased activity oftrpR promoter but does not affecttrpS ortrp promoters. The Dam-mediated induction oftrpR was, however, found to be repressed bytrpR-mediated autoregulation. In contrast,trp-lacZ directedβ-galactosidase activity was increased at least sixfold indam cells in late logarithmic growth phase. Indam + cells, expression oftrp-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 ofdam mutation. This finding is discussed in the context of the pleiotropic phenotype ofdam mutation.