D. Dressler investigated the molecular mechanism of genetic recombination. With H. Potter, the researcher examined candidate DNA intermediates directly by electron microscopy, connecting a proposed strand-exchange mechanism to observable molecular forms.[ref]
On the mechanism of genetic recombination: electron microscopic observation of recombination intermediates by H. Potter and D. Dressler. Byline and Abstract: microscopy of recombination intermediates
The 1976 study isolated Colicin E1 plasmid DNA and cut it with the restriction enzyme EcoRI. Among the preparations were crossed structures containing approximately twice the normal plasmid DNA content. Their paired-length arms supplied a more specific structural test than the presence of an arbitrary crossing in a micrograph.[ref]
On the mechanism of genetic recombination: electron microscopic observation of recombination intermediates by H. Potter and D. Dressler. Abstract and micrographs: EcoRI-linearized DNA and crossed forms
The example illustrates why sample preparation can clarify a mechanistic question. Cutting circular molecules into lengths with known endpoints makes the organization of the candidate intermediate easier to compare with the prediction. Images provide structural evidence; the interpretation still requires appropriate preparation and biological controls.
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