The Yield and Repair of X-Ray-Induced Single-Strand Breaks in the DNA of Escherichia coli K-12 Cells

Abstract
The yield of single-strand breaks present in chromosomal DNA of E. coli cells after aerobic X irradiation was determined using alkaline sucrose gradient techniques. Experimental conditions were used that avoided a centrifugation speed dependence effect on DNA sedimentation and allowed either minimal or complete enzymatic repair to occur. The extent of DNA strand breakage was previously underestimated by factors of 3.4-7.6, depending on the strain and repair conditions used. Technical and interpretive difficulties in the measurement of DNA single-strand breakage using alkaline sucrose gradient techniques are discussed briefly. In these experiments, the initial yield of DNA single-strand breaks was 32.4/genome krad-1 (9.0 eV/break).