@article{48387a6356c940ae95b7c185f2c009fe,
title = "Thymidine labeling of pyrimidine isostichs from human lymphocyte DNA during repair after damage with N-acetoxy acetylaminofluorene or nitrogen mustard",
abstract = "Evidence for the faithfulness of DNA repair in mammalian cells is presented. Human peripheral blood lymphocytes with very low background levels of DNA synthesis were prepared by using populations that are 99.8 to 99.9% free of dividing cells and by further supressing DNA synthesis in these with hydroxyurea. These cells were damaged with nitrogen mustard or the proximate carcinogen N-acetoxy-2-acetylaminofluorene and allowed to undergo repair in the presence of tritiated thymidine. Pyrimidine isostichs were prepared from the DNA by formic acid and diphenylamine digestion and were separated on DEAE-cellulose. The distribution of counts in the pyrimidine isostichs from treated and control cells was found to be the same. The latter served as a measure of the frequency of various isostichs present in the normal DNA. Thus, it is suggested that during repair, bases are incorporated in a fashion which approximates their distribution in the original DNA.",
author = "Lieberman, {M. W.} and Rutman, {Julia Z.} and E. Farber",
note = "Funding Information: apparent that, within the limits of error of the method, the distribution of counts in isostichs prepared from damaged repairing cells is the same as that seen in the replicating cells, and both are similar to the distribution of ultraviolet-absorbing material from calf thymus DNA. These results establish that, during repair, bases are incorporated in a thshion which in general approximates their distribution in the normal DNA. The method will not pick up single base deletions or substitutions or distinguish between shuffled sequences (e.g. pT-C-C-Tp for pC-T-T-Cp), but nevertheless it establishes that such possibilities as mononucleotide addition (either internal or terminal) or selective incorporation into relatively long runs of pyrimidines do not account for much, if any, of the incorporation during repair. Previous digestion studies of DNA isolated from cells during repair 13 have demonstrated that at least 80-85% of the label added as \[3H \]thymidine is incorporated internally into DNA. Our present study confirms these findings since we have not found isostichs of the form Pyr(n ) P(n) (i.e. lacking a terminal phosphate) which would be expected if substantial terminal addition or unligated sequences were present. Such isostichs, especially the monomers, would produce a significant divergence from the correspondence between absorbance and radioactivity observed in this study. This research was supported by grants from the American Cancer Society, the National Cancer Institute (CA 12218) and the Health Research and Services Foundation of Pittsburgh. One of the authors (M.W.L.) is a Sarah Mellon Scaife Fellow. Copyright: Copyright 2014 Elsevier B.V., All rights reserved.",
year = "1971",
month = oct,
day = "28",
doi = "10.1016/0005-2787(71)90036-0",
language = "English (US)",
volume = "247",
pages = "497--501",
journal = "BBA Section Nucleic Acids And Protein Synthesis",
issn = "0005-2787",
publisher = "Elsevier B.V.",
number = "3",
}