Mullis, Kary Banks (1944– )

US molecular biologist who was awarded the Nobel Prize for Chemistry in 1993 for the invention of the polymerase chain reaction (PCR) technique, which allows specific regions of DNA to be copied many times from a tiny sample, thus amplifying it to a large enough quantity to be analysed. This technique signalled an end to the laborious method of producing DNA fragments in vivo. He shared the Nobel Prize with Michael Smith.

How DNA is copied In PCR, a small sample of DNA (for example, from a blood sample) is cut into segments and denatured (broken down) into single strands. Short oligonucleotide probes complementary to the DNA are prepared, and added in large amounts to the denatured DNA, and then incubated at 50–60°C. The probe joins to its correct site on the DNA, and acts as a starting point for synthesis of a new DNA chain. After the synthesis has finished the mixture is heated to 95°C to melt the newly formed DNA duplexes. The cycle can be repeated in order to amplify the desired sequence, and in just a few hours more than 100 billion copies can be made. These can then be used for analysis. The technique is now commonly used worldwide and is particularly important for disease diagnosis, for example, in the test for HIV.

Life Mullis was born in Lenoir, North Carolina, and educated at the Georgia Institute of Technology and the University of California, Berkeley, where he obtained his PhD in 1973. After conducting research at the University of Kansas Medical School and at the San Francisco campus of the University of California, Mullis joined the Cetus Corporation of Emeryville, California, in 1979.