Repair of X-ray damage to the DNA in Micrococcus radiodurans: the effect of 5-bromodeoxyuridine

Abstract

Radiation damage to the DNA of Micrococcus radiodurans is eliminated or modified by processes which effect the rejoining of DNA strand breaks and degradation of the DNA. The enzyme system which is responsible for DNA degradation also appears to be implicated in the removal (excision) of damaged DNA constituents. Following anoxic X-irradiation the survival of the bacterium exceeds 95% at doses below 500 krads. Progressive replacement of the thymine in the cellular DNA by 5-bromouracil results in the progressive removal of the shoulder from the anoxic X-ray survival curve with little change in the slope. There does not appear to be a concomitant effect upon either the extent of DNA strand breakage or the properties of the system rejoining the breaks. However, the loss of the shoulder from the survival curve is paralleled by interference with DNA degradation. When the level of the 5-bromouracil incorporation is such that the shoulder has been eliminated from the survival curve the degradation-excision system is inoperative.