This proposed solution to a long-standing cellular mystery comes with a visual aid

It may look like some sort of strange modern art – but it’s a simple machine describing a very complicated, and mysterious, process.

Before cells divide, their DNA must be precisely copied in a process called replication. A ring-shaped enzyme called the minichromosome maintenance or MCM complex plays a central role in that process.

During DNA replication, the MCM complex is positioned at the fork where double-stranded DNA separates into single strands. Those strands are copied to produce a new DNA molecule.

As a structural biologist, my colleagues and I used state-of-the-art equipment to capture an atomic-scale image of the crystal structure of the DNA replication machinery. But I took a more creative approach to illustrate how the crystal structure may help solve a mystery at the heart of cell division: How DNA replication begins. Using scrap lumber, I built a simple machine to help visualize how double-stranded DNA encircled by separate enzyme complexes first begins to separate into single-stranded DNA, which can be copied in advance of cell division.

Our lab produced the first atomic-resolution image of the MCM complex bound to single-stranded DNA and the molecules that fuel replication. The research appears in the journal Nature Communications.

The image captured key structural details, including the orientation of both the MCM complex and single-stranded DNA. The elements illustrated how the process works like a pulley system to “pull” a single strand of DNA through the MCM complex and unwind the DNA.

The same mechanism may also explain how DNA replication begins.

About the author

Eric Enemark, PhD, is an associate member of the Structural Biology Department at St. Jude Children's Research Hospital.

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