In 1956, Arthur Kornberg isolated and identified the first DNA polymerase (Pol I) in the bacterium E. coli, demonstrating an enzyme capable of synthesizing a new complementary DNA strand from a template strand in vitro. This discovery established the basic molecular mechanism of DNA replication and was the conceptual and instrumental basis for all later techniques requiring controlled copying of genetic material, including PCR. Nobel Prize in Medicine 1959 shared with Severo Ochoa.