Unveiling the mechanism of regulation of excessive fork elongation by Polymerase Iota

Sofía Venerus Arbilla¹*, Sabrina Mansilla¹*, Agostina Bertolin¹, María Belén de la Vega¹, Vanesa Gottifredi¹ *equal contribution

To preserve the integrity of genetic information, cells must count with mechanisms—englobed by the term DNA Damage Response (DDR)—to protect cellular fitness when DNA lesions accumulate during DNA replication. DDR includes processes of tolerance to damaged DNA, like Translesion DNA Synthesis (TLS), in which alternative polymerases (Alt. Pols) release replication stalling by using damaged DNA as replication templates. We found that one Alt. Polymerase, Pol Iota, has a novel function not shared with other Alt. pols in preventing unleashed DNA elongation. In doing so, Pol iota promotes the correct onset of checkpoint signals, preventing cell death and genomic instability. How Pol iota achieves this replication effect is unknown. Pol Iota has at least three associated functions: 1) it participates promoting the bypass of DNA lesions during TLS events; 2) its lyase motif allows it to repair abasic sites in Basic Excision Repair; 3) it interacts with the tumor suppressor p53 to reduce fork elongation speed. We were able to demonstrate that TLS and DNA repair were not required but p53 was required to control defective activation of checkpoint signals. Transient expression of exogenous Pol Iota rescued the DDR defects observed in CRISPR Pol Iota KO clones. In the future, we aim to identify the domain(s) of Pol Iota required for this non-canonical role of the Alt Pol.