Electron microscopy of gene regulation: The L -arabinose operon

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Abstract
High magnification EM revealed protein complexes specifically bound to homogeneous DNA fragments containing the regulatory region of the Escherichia coli L-arabinose operon. Formation of detectable complexes on the DNA requires araC protein, catabolite gene activator protein and RNA polymerase (nucleotidyltransferase). These protein-DNA complexes appear to be involved in regulation of the operon. Incubation of the proteins and DNA under inducing conditions leads to formation of a complex that appears to be capable of transcription, whereas incubation of the proteins and DNA under repressing conditions leads to formation of a different complex incapable of transcription. Using 3 overlapping DNA fragments, the sites of complex formation on the DNA were located. The complexes are formed on sequences 108 base pairs apart, an unexpectedly large distance.