Discontinuities in the DNA synthesized in an Excision-defective strain of Escherichia coli following ultraviolet irradiation

摘要: Although Escherichia coli K12 uvrA6 is defective in the excision of pyrimidine dimers from its DNA, 37% cells survive a dose ultraviolet light which equivalent to about 50 per 107 nucleotides. The amount tritiated thymidine incorporated into DNA irradiated indicates that inhibit synthesis but are not permanent blocks. Zone sedimentation single-strand was performed alkaline sucrose gradients. To minimize degradation by shearing, released spheroplasts layered on top Newly synthesized, denatured unirradiated sediments with molecular weight greater than 100 × 106, whereas newly 60 ergs/mm2 has 14 106. During subsequent incubation cells, rate synthesized immediately after irradiation increases and approaches normal DNA. However, at any time during this period, incorporation fast-sedimenting minimal, suggesting daughter-strand ultraviolet-irradiation contains gaps, or alkalilabile bonds. These dicontinuities disappear further incubation, as higher found. number these defects similar an length parental