Depressibility of excision repair mechanism in Escherichia coli B/r Hcr+ cells

Simultaneous amino-acid and thymine starvation applied prior to UV irradiation depresses dimer excision in excision-proficient E. coli B/r Hcr+ cells. In exponentially growing cells the excision mechanism excises similar amounts of pyrimidine dimers per unit time, irrespective of the initial number of induced dimers. In prestarved cells diminution of its ability to excise dimers occurs, which is relatively equal after all tested UV doses, but absolutely dependent on the initial number of induced dimers. It is suggested that the depression of excision mechanism is due to some changes of the DNA structure rather than to an enzymatic insufficiency. (author)