Action of DNA glycosylases on chromatin structure

Nuclei of human lymphoblastoid cells NL3 incorporated dUMP into DNA in vitro. The rate and extent of this incorporation were less than those of dTMP, presumably due to the presence of dUTPase and uracil-DNA glycosylase in nuclear preparations. NL3 cell extracts released only about a half of the misincorporated uracil as free base from nuclei, their chromatin and chromatin reconstituted from dUMP-containing DNA and calf thymus chromosomal protein, though almost all uracil from reconstituted chromatin containing PBS1 phage DNA. The cell extracts also release 10-40% of 3-methyladenine from methylated nucleosome monomers and dimers, and chromatins reconstituted from methylated DNA and poly (dA . dT). The shorter molecule lost fewer 3-methyladenine.