Researchers have recorded up-close footage of a single DNA molecule replicates itself.
New footage showing DNA Replication is raising questions about how we have always assumed the process works.
The real-time footage shows this fundamental part of life involves an unexpected amount of ‘randomness’ and means we might need a major rethink on how genetic replication occurs.
It’s a real paradigm shift, and undermines a great deal of what’s in the textbooks […] It’s a different way of thinking about replication that raises new questions Stephen Kowalczykowski, Professor in microbiology and molecular genetics at the University of California, Davis
How We Thought DNA Replication Worked
Up to now, we always believed replication was driven by a three step process.
First, helicase (an enzyme) unwinds then unzips the double helix into two single strands. Next primase then attaches a ‘primer’ to each of these unravelled strands. Then finally, DNA polymerase attaches to the primer, adding an additional bases to form a whole new double helix.
Because these double helices form around two strands running in opposite directions – we have always assumed one is a ‘leading strand’ (which winds around first) and the other is the ‘lagging strand’ (which follows this leader).
We know that the final result should be an exact match to what was on the original DNA. Up to now it was assumed that these two strands coordinate with each other throughout the replication process (otherwise if one would get ahead of the other, during the unravelling, mutations might occur).
Thinking DNA Replication
The problem is that the team’s new footage show that there’s no coordination at play here at all.
The footage shows each strand acting independently of the other but still results in a perfect duplicate each time.
The team used DNA from E.coli bacteria. The resulting footage shows the speed at which the two strands replicated as (roughly) equal, but with a number of stops and starts that meant the strands did not always replicate at the same speed or in sync.
We’ve shown that there is no coordination between the strands. They are completely autonomous Stephen Kowalczykowski, Professor in microbiology and molecular genetics at the University of California, Davis
The question now is that if these strands “function independently” — how does the double helix know how to keep things on track?
The team hope to refine their technique to produce more footage and then help unwind the mystery of DNA Replication in the future.
The research has been published in Cell “Independent and Stochastic Action of DNA Polymerases in the Replisome”.