Before the COVID-19 pandemic, you may have not known about polymerase chain reaction (PCR) unless you worked in a lab using it. Even then, you may not know the wild story of its origins.
PCR has a huge array of applications – from testing for diseases, criminal investigations, paternity tests, and even sequencing human genomes. Basically, wherever scientists are working with DNA, there's a good chance PCR is involved.
PCR can take a tiny amount of DNA that would be very difficult to study and amplify it over and over into much larger quantities, allowing it to be studied more easily. Before the invention of PCR, this process was long and laborious, with scientists using cloning to amplify DNA in bacteria.
It’s considered a revolutionary technique, summed up in this reverential ode.
The person credited with inventing PCR is Dr Kary Mullis, for which he won a share of the 1993 Nobel Prize in Chemistry.
To put it lightly, Dr Mullis was considered by many in the scientific community to be a controversial and problematic figure, described as an “interpersonal wrecking ball” in California Magazine.
“In the midst of being extremely charming, he could be extremely abusive,” his friend and colleague Dr Thomas J White told The New York Times. During an interview with Esquire, Mullis repeatedly touches the interviewer and attempts to convince her to sleep with him, even after she says no. She would later describe him as “outrageous” and “nasty.”
He also had his fair share of odd (and plain wrong) scientific opinions – for example, he did not believe that humans cause climate change, or that HIV causes AIDS. His colleagues noted that he often made errors with basic biology when coming up with ideas.
Dr Mullis died aged 74 on August 7, 2019, from respiratory and heart failure resulting from pneumonia. However, to look at how he came up with PCR, we’re traveling back to May 1983.
The Deoxyribonucleic Acid Trip
As he recounts in his book Dancing Naked in the Mind Field, Mullis was driving his silver Honda through California, heading from Berkeley to his cabin in Anderson Valley. It was a Friday. At this time, Mullis was employed at Cetus, a biotechnology company. He worked with oligonucleotides: short strings of nucleotides, which are the building blocks of DNA and RNA.
As he drove, his brain started to get creative. “DNA chains coiled and floated. Lurid blue and pink images of electric molecules injected themselves somewhere between the mountain road and my eyes,” he recounted.
Mullis stated that he was “functionally sober” at this point – however, his famous love for taking and making the psychedelic drug LSD gives these colorful scenes a whole other context. In fact, he once said “Would I have invented PCR if I hadn’t taken LSD? I seriously doubt it […] I could sit on a DNA molecule and watch the polymers go by. I learnt that partly on psychedelic drugs.”
Albert Hoffman, who discovered LSD, has said that Mullis personally told him that the psychedelic had helped him conjure up the concept of PCR.
As the DNA danced in his mind’s eye, Mullis thought of how two oligonucleotides could stick to either end of a short area of interest in a comparatively vast string of genetic material.
His computer programming experience also drifted into view, and he started to consider how he could apply a reiterative mathematical procedure to this process. This would mean that after the area of interest was marked by the oligonucleotides, the natural tendency of DNA to replicate itself could be harnessed to reproduce this area of interest over and over and over and over.
Mullis stopped the car, pulled off the road, and started scribbling his ideas on an envelope so enthusiastically that he broke the lead of his pencil.
Testing The Idea OF PCR
This brainwave wasn’t left in the driver’s seat of his car. Mullis wrote that “We got to my cabin and I started drawing little diagrams on every horizontal surface that would take pen, pencil, or crayon, until dawn.”
Now he had to prove his idea.
He presented his ideas at a Cetus seminar in August 1983, to a skeptical response.
“People don’t believe things, usually, for the right reasons,” Mullis said in a Google TechTalk in 2010. “The reason they didn’t believe this was because of the fantastic result of it. Not because any one of the steps was unlikely to work.”
"He got a lot of data but he was having personal problems and tended to do uncontrolled experiments, so it wasn't very convincing when he did get a result,” Dr White told the New York Times.
In fact, his first attempt at PCR was unsuccessful. He had attempted to use the technique to amplify a fragment of Human Nerve Growth factor, the sequence of which had been recently published. However, scientists at Cetus persisted for months alongside Mullis to create a proper experimental system to make it work.
Mullis writes that the first successful attempt at PCR was on December 16, 1983. His colleague Fred Faloona had helped to set up the reaction. Rather than using human DNA, Mullis had settled on using a plasmid, a simpler type of bacterial DNA.
The process would end up utilizing Taq DNA polymerase, an enzyme from a bacteria found in Yellowstone National Park hot springs called Thermus aquaticus. This is important as high temperatures are required in each round of DNA amplification, and Taq DNA polymerase can withstand the heat. Thanks to its role in PCR, the enzyme was crowned "Molecule of the Year" by Science in 1989.
In 1985, the team published a paper in the journal Science outlining how they used PCR to amplify human DNA as a potential way to diagnose sickle cell anemia.
An application to patent PCR was filed by Cetus in 1986, with Mullis applying for a patent in 1985. Both patents were granted in 1987.
However, Dr Mullis left Cetus in 1986. He had been paid $10,000 for his part in discovering PCR, but this pales in comparison to the $300 million Cetus sold the rights for five years later.
As Kary Mullis wrote in his book, “It would spread into every biology lab in the world. I would be famous. I would get the Nobel Prize.” This was one idea that was absolutely correct.