Matthew Meselson

Matthew Meselson is an American molecular biologist whose experiments with Franklin Stahl established semiconservative DNA replication and whose later work helped reveal genetic recombination.

Meselson–Stahl experiment: A 1958 experiment using nitrogen isotopes to distinguish models of DNA replication in Escherichia coli. Meselson and Franklin Stahl used density gradients to show that each daughter DNA molecule retains one parental strand.
Franklin Stahl: An American geneticist who co-designed the Meselson–Stahl experiment with Matthew Meselson. Stahl was Meselson’s partner in the experiment that established semiconservative DNA replication.
Semiconservative replication: DNA replication in which each daughter double helix contains one parental strand and one newly synthesized strand. This is the replication mechanism supported by the intermediate-density DNA observed after one generation.
Holliday junction: A four-stranded DNA structure formed when homologous DNA molecules exchange strands. Meselson’s research on recombination helped connect genetic exchange to physical DNA intermediates.
Density-gradient centrifugation: A technique that separates molecules according to their buoyant density in a centrifugal field. It separated DNA containing heavy nitrogen from DNA containing light nitrogen in the landmark replication experiment.
Linus Pauling: An American chemist who proposed influential models of molecular structure, including an incorrect triple-helix model of DNA. Meselson and Stahl designed their replication test amid competing structural models of DNA.
Conservative replication: A proposed DNA-copying model in which the parental double helix remains intact while a wholly new helix is made. It predicted separate heavy and light DNA after one generation, unlike the observed hybrid molecules.
Bacteriophage lambda: A virus that infects Escherichia coli and is widely used to study gene regulation and recombination. Meselson and colleagues used lambda phage in studies of DNA recombination.
DNA replication: The cellular process of copying DNA before cell division. The experiments established how parental DNA strands are distributed during replication.
James Watson: An American molecular biologist who, with Francis Crick, proposed the double-helix structure of DNA. The double helix suggested a copying mechanism whose predictions Meselson and Stahl tested.

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