Concept 20 A half DNA ladder is a template for copying the whole.

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Matthew Meselson and Franklin Stahl invented the technique of density gradient centrifugation and used this to prove that DNA is replicated semi-conservatively. Arthur Kornberg identified and isolated DNA polymerase I — one of the enzymes that can replicate DNA.

Franklin "Frank" Stahl was born in Boston. He received a B.A. from Harvard University in 1951. Stahl then went to the University of Rochester for graduate work.

While finishing up his Ph.D., Stahl attended a molecular biology course at Woods Hole. The course was being taught by James Watson and Francis Crick, and it was here that Stahl met Matthew Meselson. As they both tell it, during a break in the course, Meselson introduced himself to Stahl who was sitting under a big tree drinking and selling gin and tonics. At the time, Meselson was a graduate student at the California Institute of Technology; he was interested in exploring new methods of experimentation. Stahl had the experience and the math to help Meselson design these experiments. They hit it off right away and made plans for Stahl to do post-doctoral work at Caltech.

In 1957, Stahl and Meselson developed the technique of density gradient centrifugation and used it to prove that DNA was replicated in a semi-conservative way, as predicted by Watson and Crick in their 1953 paper. Meselson and Stahl's paper appeared in 1958.

In 1959, Stahl accepted a position at the University of Oregon where he is still a distinguished Emeritus P rofessor of Molecular Biology. He maintains a research interest on the mechanisms of genetic recombination.