DNA repair in Escherichia coli: the dual function of uvr genes

It has been shown earlier that the starvation of E. coli for both amino-acids and thymine applied prior to UV irradiation inhibits pyrimidine dimer excision without affecting cell survival after UV irradiation. In such cells pyrimidine dimers are tolerated by a rather error-free process that depends on the activity of uvrB, recA and lexA genes. Data presented here show: (a) that the efficient toleration of unexcised dimers requires also the uvrA gene; (b) that the starvation increases the level of RecA protein about 4.7 times; (c) that the effect of starvation on subsequent pyrimidine dimer excision is reversed by a 2 h incubation in complete medium before the cells are UV irradiated. The data suggest that the uvrA, uvrB, recA, lexA dependent nonexcisional repair may be a pathway temporarily functioning in repeatedly damaged cells.