Biochemist received Nobel Prize for invention of PCR and attracted controversy for positions on climate change and AIDS
by Celia Henry Arnaud
Chemical & Engineering News
Kary B. Mullis, Nobel Laureate in Chemistry, died Aug. 7 of pneumonia at the age of 74. He won the 1993 Nobel Prize in Chemistry for his invention of the polymerase chain reaction (PCR) method for copying and amplifying DNA. Mullis invented the PCR method in 1983 as a chemist at Cetus Corporation.
The original version of PCR that Mullis developed uses repeated cycles of elevated temperatures to separate DNA strands, which are then copied by a heat-stable DNA polymerase. Repeating the cycle many times leads to an exponential increase in the quantity of DNA. In this way, even traces of DNA can be amplified into amounts that can be easily sequenced or quantified.
PCR amplification played a key role in the Human Genome Project, in which most of the DNA blueprint of one person was sequenced.
“The initial scientific goals of the Human Genome Project were actually established before PCR had become a routine laboratory method,” says Eric D. Green, director of the National Human Genome Research Institute at the National Institutes of Health and participant in the Human Genome Project. “In retrospect, the widespread development of PCR-based methods ultimately turned out to be critical—in many ways essential—for the Project’s success.”
PCR also made its mark in forensic science. “Prior to the development of the PCR, forensic scientists utilized very awkward and insensitive techniques” to identify people from DNA samples, says Bruce McCord, a professor of forensic chemistry at Florida International University. “The development of the PCR revolutionized forensic DNA testing. Suddenly there was no need for radioactivity or chemiluminescence-based detection, as the PCR could produce millions of copies of DNA from only a few cells.”
Beyond his work on PCR, Mullis was also known for his controversial views disputing humans’ role in climate change and HIV’s role in AIDS. He also was open about taking hallucinogenic drugs like LSD and synthesizing some when in graduate school.
Mullis was born in Lenoir, North Carolina, in 1944. He received a bachelor’s degree in chemistry from the Georgia Institute of Technology in 1966 and a PhD in biochemistry from the University of California, Berkeley, in 1972. He joined Cetus in 1979. In 1986, he became the director of molecular biology at Xytronyx. And starting in 1987, he worked as a consultant on nucleic acid chemistry for multiple companies.
He is survived by his wife, three children, and two grandchildren.
***In the US, the FDA’s instructions for PCR testing recommends a threshold of ***40 cycles for a specimen to be considered positive. See page 35 of the instructions…
At 25 cycles the original material has been multiplied 33,554,432 times.
At 30 cycles the original material has been multiplied 1,073,741,824 times.
At 40 cycles the original material has been multiplied 1,099,511,627,776 times.
As you can see there is quite a difference in magnification at various cycle thresholds.
It is also important to remember PCR was invented as a way to create copies of genetic material. Its was never intended to be a diagnostic tool.