UC San Diego

RNA polymerase II (pol II) recognizes many obstacles during transcription elongation, including DNA damage lesions and modifications, via specific interactions and leads to distinct transcriptional outcomes. We investigate three specific types of modifications/lesions in DNA and how they affect the pol II transcription process: 1) unnatural synthetic nucleotides (dNaM and dTPT3), 2) regioisomeric alkylated thymidine lesions (O2-, N3-, O4-EtdT), and 3) non-covalent minor groove DNA binders pyrrole-imidazole (Py-Im) polyamides. In Chapter 1, we investigate pol II transcription and elongation in the presence of synthetic nucleotides (dNaM and dTPT3), and the ability of pol II to distinguish between natural NTPs and the unnatural triphosphates. Selective incorporation of rNaM by pol II only occurs when dTPT3 is in the template strand, and loses its selectivity when dNaM is in the template. In Chapter 2, we discovered distinct patterns of pol II transcriptional bypass for each of the alkylated thymidine lesions. We found that pol II bypass of O2-EtdT is essentially error free, bypass of O4-EtdT is efficient and highly error prone, and bypass of N3-EtdT is extremely slow. In Chapter 3, we found that Py-Im polyamides bound to the minor groove at sequence specific sites causes prolonged pol II arrest upstream of the binding site, due to two specific residues in the pol II Switch 1 region that contribute to the early detection of the obstruction in the minor groove. Taken together, these studies highlight the importance of pol II recognition of DNA damage and modifications in the maintenance of transcriptional fidelity.