Kavi Mehta

Replication-Coupled DNA Repair, Mutagenesis, and Genome Maintenance

Strand-specific replication stress and DNA damage tolerance
Research in the Mehta lab investigates how cells detect, tolerate, and repair DNA damage that arises during replication. We focus on the asymmetry between leading and lagging strand stress responses, the regulation of translation synthesis polymerases, and the mechanisms by which viruses like HPV exploit the replication stress machinery for their own ends. Defects in these pathways drive genome instability and mutagenesis at the root of cancers. We combine cell-based genetic systems, proteomics, single-molecule biochemical approaches, and strand-specific sequencing approaches to answer mechanistic questions with direct relevance to human diseases.

The replisome
Every time a cell divides, it must duplicate its entire genome with remarkable speed and accuracy. This task falls to the replisome, a large multiprotein machine that assembles at replication origins and coordinates the unwinding, priming, and synthesis of new DNA strands. At its core is a replicative helicase that separates the duplex ahead of the fork, coupled to DNA polymerases that copy the leading and lagging strands simultaneously. Surrounding this core is a dynamic assembly of accessory factors that regulate polymerase fidelity, respond to DNA damage, coordinate replication with repair, and ensure that the genome is duplicated faithfully. When the replisome has defects, the consequences are profound: mutations accumulate, chromosomes break, and cells lose the genomic integrity that is essential for normal function. The Mehta lab uses iPOND as an unbiased tool to capture proteins physically associated with newly synthesized (nascent) DNA, coupled with quantitative mass spectrometry-based proteomics, to define the composition and dynamics of the replisome under normal and stressed conditions. Understanding how the replisome is assembled, regulated, and its make-up under different conditions is central to understanding cancer, aging, and the basic biology of every dividing cell.

Defining strand-specific replication stress responses
DNA replication is inherently asymmetric, yet the checkpoint machinery that responds to replication stress has largely been studied without regard to which strand is under threat in humans. The Mehta lab investigates whether the cellular response to replication stress differs depending on where that stress arises, and what the consequences of that asymmetry are for genome stability. Resolving these questions has fundamental implications for how we understand mutagenesis, fork restart, and the origin of replication-associated genome instability in cancer as well as guiding therapeutic interventions.

Understanding acute regulatory mechanisms of specialized DNA polymerases
When the replication fork encounters a DNA lesion it cannot bypass, cells can encode for a variety of specialized polymerases known as translation polymerases to continue replication across damaged templates. How these enzymes are recruited, activated, and restrained in a damage-dependent manner is poorly understood. The Mehta lab takes a biochemical and cell biological approach to defining the regulatory logic that governs their activity, and to understanding how cells choose between different damage tolerance strategies in a context-dependent way.

Understanding how small tumor viruses like HPV remodel the host replisome and alter mutagenic potential
Human papillomavirus must amplify its genome inside a host cell that has largely exited the cell cycle. To do so, it commandeers the host replication machinery, and the consequences of that hijacking for the integrity of the host genome remain poorly understood. The Mehta lab investigates how HPV remodels the host replisome to support viral replication, and how that remodeling shifts the mutational landscape in ways that may contribute to HPV-associated malignancy.

Defining the replisome in all organisms, microbes, and models
The core challenge of genome duplication is solved differently across the tree of life. The Mehta lab has a broad interest in the composition, architecture, and regulation of replisome complexes across models from archaeological to animals. By comparing how different organisms assemble and regulate their replisomes, we aim to identify conserved principles of replication fidelity and stress response, as well as evolutionary innovations that illuminate the pressures acting on genome maintenance systems.