Distribution Within Chromatin of Deoxyribonucleic Acid Repair Synthesis Occurring at Different Times After Ultraviolet Radiation

We have compared the initial distribution and subsequent redistribution within chromatin of nucleotides incorporated during the early ("rapid") phase and the late ("slow") phase of UV-induced DNA repair synthesis. As has been observed for the early repair phase, most or all of the nucleotides incorporated during the late repair phase are initially staphylococcal nuclease and DNase I "sensitive" (i.e., rapidly digested). This initial enhanced sensitivity is accompanied by both an underrepresentation of these nucleotides in the 145-165 base pair (core) DNA produced by staphylococcal nuclease digestion and an absence of these nucleotides in the ∼10-base repeat pattern produced by DNase I digestion. Furthermore, nucleotides incorporated at late times after damage are involved in nucleosome rearrangement as reported previously for repair synthesis occurring at early times [Smerdon, M. J., & Lieberman, M. W. (1978) Proc. Natl. Acad. Sci. U.S.A. 75, 4238-4241]. The kinetics of redistribution, however, appear to be more rapid than those observed for early times. Following redistribution the average nucleosome repeat length of DNA containing repair-incorporated nucleotides is the same as that of bulk DNA regardless of the time after damage that repair occurs; also, many of these nucleotides coelectrophorese with the ∼10-base repeat fragments generated by DNase I. These results yield a new interpretation of our previous studies [Smerdon, M. J., Tlsty, T. D., & Lieberman, M. W. (1978) Biochemistry 17, 2377-2386] on the distribution of nucleotides incorporated at long times after UV irradiation.