Direct Measurement of DNA Unwinding Angle in Specific Interaction between lac Operator and Repressor
This extract was created in the absence of an abstract.
Excerpt
The affinity between DNA and protein in sequence-specific interaction often varies depending on the superhelical density of the DNA. Small variation has been observed in, for example, the binding of bacteriophage λ repressor to its operator (Maniatis and Ptashne 1973), lactose (lac) repressor to its operator (Wang et al. 1974), and EcoRI restriction enzyme to its cognate DNA sequence (P. Modrich, pers. comm.). These variations may play an important role in the regulation of the biological functions of these proteins.
In general, these proteins bind slightly better to supercoiled DNA than to relaxed DNA that contains the cognate sequence. This can be interpreted as due to small unwinding of the recognized DNA upon protein binding. Direct measurement of such small winding or unwinding angles is difficult.
We report here the direct measurement of unwinding angle in the lac repressor-operator interaction using a stable plasmid constructed to contain multiple copies of...
