PCR (1): Background

Polymerase chain reaction was invented by Kary Mullis in April 1983. Mullis has written that he conceived PCR while cruising along the Pacific Coast Highway 128 one night in his Honda Civic. He was playing in his mind with a new way of analyzing mutations in DNA when he realized that he had instead invented a method of amplifying any given DNA region. Mullis has stated that LSD helped him to conceive of PCR.

He was awarded the Nobel Prize in Chemistry in 1993 for his invention, only seven years after his proposal became practice. Mullis's idea was to develop a process by which DNA could be artificially multiplied through repeated cycles of duplication driven by DNA polymerase.

This works by binding to a single DNA strand and creating the complementary strand. In Mullis's original process, the enzyme was used in vitro. The double-stranded DNA was separated into two single strands by heating it to 94°C. At this temperature, however, the DNA polymerase used at the time was destroyed, so the enzyme had to be replenished after the heating stage of each cycle. Mullis's original procedure was very inefficient, since it required a great deal of time, large amounts of DNA polymerase, and continual attention throughout the process.

Later, this original PCR process was greatly improved by the use of DNA polymerase taken from thermophilic bacteria grown in geysers at a temperature of over 110°C. The DNA polymerase taken from these organisms is stable at high temperatures and, when used in PCR, does not break down when the mixture was heated to separate the DNA strands. Since there was no longer a need to add new DNA polymerase for each cycle, the process of copying a given DNA strand could be simplified and automated.