Arthur Kornberg (1957) → Discovered DNA Polymerase (enzyme responsible for synthesising DNA)
Isolated enzyme that synthesised DNA, called DNA polymerase.
Created a cell-free system that replicated DNA, to test out the experiment.
Extracted DNA polymerase from E.coli, then added it to a salt solution containing template DNA strand and 4 deoxynucleotides, the thymine was radioactively labelled (this used to monitor the new DNA mol that were made).
After incubating these components at body temp, the radioactive thymine turned up in long polynucleotides, hence DNA polymerase had incorporated the radioactive thymine, along with other nucleotides and built a new strand against the template strand.
He also found that replication only occurs when all 4 nucleotides are present. If one omitted, then polynucleotide chain not synthesised.
He further found that DNA polymerase required intact DNA to serve as a template (by adding DNase which digested the template DNA into pieces and polynucleotide production was halted).
So, as Watson and Crick had predicted, DNA is used as a template to replicate itself and DNA polymerase is the enzyme that makes it happen (discovered by Kornberg).
Later it was found that cells have 3 different DNA polymerases, the one discovered by Kornberg was DNA polymerase I (used mostly for DNA repair and not DNA replication). DNA polymerase III, isolated by his son, is the major enzyme that replicates DNA in E.coli.
Reference: https://www.dnalc.org/resources/nobel/kornberg_a.html → very good website, with pictures.