| Abstract: | We have reported previously that immediately following nucleotide excision repair in human cells the newly repaired DNA lacks a nucleosome conformation Smerdon, M. J., & Lieberman, M. W. (1980) Biochemistry 19, 2992-3000]. In this study, we have examined the ability of these nascent DNA regions to acquire a nucleosome structure in vitro by incubating intact or H1-depleted nuclei in buffers containing different salt concentrations (0.025-0.625 M KCl) at 0 or 37 degrees C. Nucleosomes were detected in these regions by an increase in the level of repair-incorporated nucleotides associated with isolated nucleosome core particle DNA. Our results indicate that the nascent DNA is resistant to nucleosome formation during the low-salt transition where the limiting repeat length decreases from approximately 190 to 168 base pairs (bp) Watkins, J. F., & Smerdon, M. J. (1985) Biochemistry (preceding paper in this issue)]. This result provides further evidence that the nascent DNA is indeed in a nonnucleosomal state. At higher salt concentrations (greater than 0.4 M), where the nucleosome repeat length decreases to a limiting value of approximately 146 bp, there was an increase in nucleosome formation in nascent DNA that correlated with the decrease in limiting repeat length. However, we did not observe a complete randomization of the repair-incorporated nucleotides. Indeed, even at the highest salt concentration used (0.625 M), we never observed more than 50% of the nascent DNA associated with the isolated core particles. This was the case even though a major portion of the nucleosomes had a limiting value repeat length following the high-salt incubation.(ABSTRACT TRUNCATED AT 250 WORDS) |
