The Role of Specific Amino Acid Residues in the Active Site of Escherichia coli DNA Polymerase I on Translesion DNA Synthesis Across from and Past an N-2-Aminofluorene Adduct

• Published in: Biochemistry (Easton) 2007-03, Vol.46 (10), p.2599-2607
• Main Authors: Lone, Samer, Romano, Louis J
• Format: Article
• Language: English
• Subjects: 2-Acetylaminofluorene - chemistry; Binding Sites; DNA - biosynthesis; DNA Adducts - metabolism; DNA Polymerase I - chemistry; DNA Polymerase I - metabolism; Escherichia coli; Escherichia coli - genetics; Escherichia coli - metabolism
• ISSN: 0006-2960; 1520-4995
• DOI: 10.1021/bi061324o

Understanding how carcinogenic DNA adducts compromise accurate DNA replication is an important goal in cancer research. A central part of these studies is to determine the molecular mechanism that allows a DNA polymerase to incorporate a nucleotide across from and past a bulky adduct in a DNA template. To address the importance of polymerase architecture on replication across from this type of bulky DNA adduct, three active-site mutants of Escherichia coli DNA polymerase I (Klenow fragment) were used to study DNA synthesis on DNA modified with the carcinogen N-2-aminofluorene (AF). Running-start synthesis studies showed that full-length synthesis past the AF adduct was inhibited for all of the mutants, but that this inhibition was substantially less for the F762A mutant. Single nucleotide extension and steady-state kinetic experiments showed that the Y766S mutant displayed higher rates of insertion of each incorrect nucleotide relative to WT across from the dG−AF adduct. This effect was not observed for F762A or E710A mutants. Similar experiments that measured synthesis one nucleotide past the dG−AF adduct revealed an enhanced preference by the F762A mutant for dG opposite the T at this position. Finally, synthesis at the +1 and +2 positions was inhibited to a greater extent for the Y766S and E710A mutants compared with both the WT and F762A mutants. Taken together, this work is consistent with the model that polymerase geometry plays a crucial role in both the insertion and extension steps during replication across from bulky DNA lesions.