Contacts between the lac repressor and the thymines in the lac operator

Area of Science:

• Molecular Biology
• Biochemistry
• Genetics

Background:

• The lac repressor protein regulates the lac operon.
• Understanding protein-DNA interactions is crucial for gene regulation studies.

Purpose of the Study:

• To pinpoint specific contact sites between the lac repressor and the lac operator DNA sequence.
• To map the physical proximity of the repressor to the DNA bases.

Main Methods:

• Bromouracil substitution for thymines in a lac operator DNA fragment.
• Ultraviolet irradiation to induce DNA crosslinking.
• Analysis of UV-induced DNA breaks using denaturing polyacrylamide gel electrophoresis.

Main Results:

• UV irradiation induced DNA breaks at bromouracil sites.
• In the presence of lac repressor, breaks at specific sites were inhibited.
• This inhibition indicates DNA crosslinking to the repressor at these locations.

Conclusions:

• Identified precise contact points between lac repressor and lac operator DNA.
• Demonstrated that the repressor protein lies close to thymine methyl groups in the DNA's major groove.