Dutta, ShuchismitaLi, YingJohnson, DonaldDzantiev, LeonidRichardson, Charles C.Romano, Louis J.Ellenberger, Tom2019-10-052004Dutta, S., Y. Li, D. Johnson, L. Dzantiev, C. C. Richardson, L. J. Romano, and T. Ellenberger. 2004. “Crystal Structures of 2-Acetylaminofluorene and 2-Aminofluorene in Complex with T7 DNA Polymerase Reveal Mechanisms of Mutagenesis.” Proceedings of the National Academy of Sciences 101 (46): 16186–91. https://doi.org/10.1073/pnas.0406516101.0027-84240744-28311091-6490http://nrs.harvard.edu/urn-3:HUL.InstRepos:41483358The carcinogen 2-acetylaminofluorene forms two major DNA adducts: N-(2'-deoxyguanosin-8-yl)-2-acetylaminofluorene (dG-AAF) and its deacetylated derivative, N-(2'-deoxyguanosin-8-yl)-2-aminofluorene (dG-AF). Although the dG-AAF and dG-AF adducts are distinguished only by the presence or absence of an acetyl group, they have profoundly different effects on DNA replication. dG-AAF poses a strong block to DNA synthesis and primarily induces frameshift mutations in bacteria, resulting in the loss of one or two nucleotides during replication past the lesion. dG-AF is less toxic and more easily bypassed by DNA polymerases, albeit with an increased frequency of misincorporation opposite the lesion, primarily resulting in G --> T transversions. We present three crystal structures of bacteriophage T7 DNA polymerase replication complexes, one with dG-AAF in the templating position and two others with dG-AF in the templating position. Our crystallographic data suggest why a dG-AAF adduct blocks replication more strongly than does a dG-AF adduct and provide a possible explanation for frameshift mutagenesis during replication bypass of a dG-AAF adduct. The dG-AAF nucleoside adopts a syn conformation that facilitates the intercalation of its fluorene ring into a hydrophobic pocket on the surface of the fingers subdomain and locks the fingers in an open, inactive conformation. In contrast, the dG-AF base at the templating position is not well defined by the electron density, consistent with weak binding to the polymerase and a possible interchange of this adduct between the syn and anti conformations.en-USJournal Article2019-10-0510.1073/pnas.0406516101