History
The identification and partial purification by Arthur Kornberg and his colleagues in 1956 of an enzyme, the DNA polymerase I of Escherichia coli, that catalysed the stable incorporation of deoxyribonucleotides into DNA in vitro came as a surprise. At the time, most scientists in the field believed that DNA synthesis was too complicated to be accurately reflected outside the living cell.
References
Friedberg EC. The eureka enzyme: the discovery of DNA polymerase. Nat Rev Mol Cell Biol. 2006 Feb;7(2):143-7. PMID: 16493419