JUN 15, 2017 05:33 PM PDT

A Completely new Look at DNA Replication

WRITTEN BY: Carmen Leitch

Scientists have gotten a close look at a process that is fundamental to life on earth - DNA replication. Reporting in Cell, the researchers observed the replication of an individual molecule of DNA, and what they saw surprised them. There was a randomness to the process they did not expect.

DNA / Credit: Nogas1974/Wikipedia

"It's a different way of thinking about replication that raises new questions," said Stephen Kowalczykowski, Distinguished Professor in Microbiology and Molecular Genetics at the University of California, Davis.

During replication, the two strands that comprise the helix of DNA are unwound. Primers then move in to get the process started, and polymerase enzyme then begins the work of adding nucleotide bases to the new, growing strand of DNA. The two strands of DNA are a little different, however, because they run in opposite directions. As such, in one direction the polymerase moves along uninterrupted, while on the other the polymerase does not work continuously, and has to hop on and off of what is called the lagging strand.

It has been thought that there was some coordination of the replication, and one polymerase did not get that far ahead of the other. The results from this new work suggest that things actually work a little differently.

The investigators set up the replication in a flow chamber, and the DNA could tsretch out. They controlled the process by adding or removing fuel in the form of adenosine triphosphate, or ATP. A fluorescent dye that binds only to double-stranded DNA highlighted the new strands as they grew.

The investigators found that replication would unpredictably come to a halt, then start up again at a different speed. "The speed can vary about ten-fold," Kowalczykowski explained. They saw that the synthesis of the lagging strand might stop completely while the leading strand grew on, leaving a portion of single stranded DNA without dye attached.

"We've shown that there is no coordination between the strands. They are completely autonomous," Kowalczykowski noted. Random starts, stops and variable speeds were observed, although there was a similar average speed of replication overall, leading Kowalczykowski to use traffic on a freeway as an analogy. "Sometimes the traffic in the lane one over is moving faster and passing you, and then you pass it. But if you travel far enough you get to the same place at the same time.”

They also saw that a kind of automatic brake was working on the enzyme that unwinds the DNA strands at the start, called helicase. It actually slows down when the polymerase does, so that it keeps working while the other enzymes get back on track, and doesn’t leave unwound portions of DNA exposed during the. lag time.

The researchers feel this work will have a major impact. "It's a real paradigm shift, and undermines a great deal of what's in the textbooks," Kowalczykowski said.

Sources: AAAS/Eurekalert! via UC Davis, Cell

About the Author
  • Experienced research scientist and technical expert with authorships on 28 peer-reviewed publications, traveler to over 60 countries, published photographer and internationally-exhibited painter, volunteer trained in disaster-response, CPR and DV counseling.
You May Also Like
SEP 16, 2019
Cell & Molecular Biology
SEP 16, 2019
Scratching a Chronic Itch
There are many potential reasons why skin might itch, but this annoying condition can significantly impact quality of life when it doesn't go away....
SEP 16, 2019
Cell & Molecular Biology
SEP 16, 2019
Insight Into a DNA Damage Sensor That Orchestrates Repair
Simple cell functions like division or metabolism can lead to DNA damage, which can also occur because of normal exposure to the sun or noxious agents....
SEP 16, 2019
Cell & Molecular Biology
SEP 16, 2019
A New Type of Cellular Communication is Discovered
While in a group, individual spirostomum can make ultrafast contractions in a coordinated fashion, without using chemical signals or contact....
SEP 16, 2019
Genetics & Genomics
SEP 16, 2019
Rethinking What we Know About Gene Control
Researchers are taking a new look at how the cell regulates gene expression....
SEP 16, 2019
Cell & Molecular Biology
SEP 16, 2019
How the Sun's Rays Damage the Skin
We all need sunlight, but it's very easy to get too much. Sunlight is the main source of the ultraviolet radiation we're exposed to....
SEP 16, 2019
Microbiology
SEP 16, 2019
Researchers Reconstruct the HIV Genome From a Sample Taken in 1966
Now there is biological evidence that the virus infected people in Africa before it was identified in the US....
Loading Comments...