Proc. Natl. Acad. Sci. USA Vol. 75, No. 9, pp. 4238-4241, September 1978 Biochemistry

Nucleosome rearrangement in human chromatin during UV-induced DNA repair synthesis (carcinogenesis/mutagenesis/staphylococcal nuclease)

MICHAEL J. SMERDON AND MICHAEL W. LIEBERMAN* Department of Pathology, Washington University School of Medicine, St. Louis, Missouri 63110

Communicated by Oliver H. Lowry, June 26,1978

ABSTRACT The distribution of UV-induced DNA repair synthesis within chromatin was measured in confluent human fibroblasts that were pulse-labeled with [3HldThd (10 or 90 min) immediately after irradiation and chased in nonradioactive medium for different time periods. Initially (i.e., at the end of the pulse period), most of the repair synthesis occurs in staphylococcal nuclease-sensitive regions. With increasing chase times the nucleotides inserted during repair synthesis become progressively more nuclease resistant. Gel electrophoresis data indicate that nuclease resistance is conferred on these nucleotides by their appearance in core DNA. The kinetics of this rearrangement process are biphasic: >85% of the repair synthesis sites undergo rapid rearrangement (4-5 hr); the remaining sites (