dna replication

There’s a Fork in DNA Replication, and Pol Theta Takes It

Posted on by Elise Johnson

In March 2026, a paper in Molecular Cell revised the understanding of a cancer target whose inhibitors are already being tested in patients. That target is Pol theta, an enzyme nearly every cell has, there to patch breaks in damaged DNA. This repair job has made it a clinical-stage drug target for years: cells that can’t repair their DNA tend to die, and cancer cells, which rack up far more damage than normal cells, are especially vulnerable to losing that option. That’s the kind of established model a field builds whole drug programs on.

Those programs include trials enrolling patients right now, testing Pol theta inhibitors in BRCA-mutant tumors and others that have lost homologous recombination (HR), a different, generally more reliable way of repairing broken DNA than the one Pol theta handles. Losing HR alone doesn’t kill these tumor cells, since they still have Pol theta’s pathway to fall back on. Take that away too, and a cancer cell that’s already down to one option for fixing this kind of damage also loses its last chance of surviving it. Scientists call this synthetic lethality.

This year, two independent labs, researching different questions, found that Pol theta plays a different role than assumed.

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Under Pressure: The Nuclear Choreography upon Replicative Stress

Posted on by Promega

Today’s blog is guest-written by Jana Krietsch (University of Zurich), edited by Nour Mozaffari (Promega)

Each time a cell divides, it must make an accurate copy of its entire genome—in human cells, this means roughly 6.2 billion individual DNA building blocks to duplicate. This enormous molecular task takes place inside the nucleus, a crowded, highly organized, yet remarkably dynamic environment. As the DNA-copying machinery moves along the genome, it may encounter roadblocks such as damaged DNA, sequences that are difficult to copy, tightly packed chromatin, or other molecular processes using the same DNA at the same time. These obstacles can slow or stall replication, a phenomenon known as DNA replication stress.

A Hidden Vulnerability of Cancer Cells

Cells are well equipped to deal with replication stress. Depending on the type and severity of the problem, they activate specialized signaling and repair mechanisms that protect replicating DNA. Failure of these responses can jeopardize genome integrity and result in permanent genetic changes that contribute to disease development.

In cancer, oncogenic changes and rapid proliferation places tumor cells under persistent replication stress. This promotes genome instability, a cancer hallmark, and drives tumor evolution. At the same time, it makes cancer cells hyper-dependent on replication stress response mechanisms to survive, creating a hidden vulnerability. Several treatments exploit this Achilles’ heel by increasing replication stress levels beyond what cancer cells can tolerate.

From Sequential Model to Dynamic Choreography

Many stress response pathways have been successfully reconstituted in the test tube. They are typically described as linear sequence of events triggered when an active replication site, termed replication fork, encounters a roadblock: the fork encounters an obstacle, its structure changes, signaling proteins are activated, repair factors are recruited, and DNA synthesis eventually resumes.

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