The expression of Escherichia coli SOS genes recA and uvrA is inducible by polyamines

Polyamines are polycationic compounds that have been implicated in a variety of cellular processes. We first report that the expression of recA and uvrA genes in Escherichia coli is inducible by polyamines. The recA and uvrA genes were effectively inducible by spermine (tetra-amine) and less effectively inducible by spermidine (tri-amine). On the other hand, both genes were not significantly inducible by putrescine (diamine) and divalent cation Mg(2+). The expression of both genes was dependent on the charge of the polyamine in the order of spermine (+4), spermidine (+3), and putrescine (+2). The induction of recA and uvrA genes by polyamines showed a dose-dependent relationship and no synergistic effects. Introduction of gyrA mutation conferring DNA relaxation increased the basal expression of recA gene about 2.5-fold compared to the wild type, but did not significantly affect the polyamine-dependent induction ratios of the recA gene. The basal and the polyamine-dependent expression of uvrA gene are not dependent on gyrA mutation. These results suggest that the polyamine-dependent expression of recA and uvrA genes may be regulated in a different way. Our results indicated that polyamines are involved in the SOS induction of recA and uvrA genes at transcriptional levels in E. coli.