LacI Bound to DNA

3D Structure of LacI Bound to lacO Promoter

CPK Color Scheme C O N P

On this page, you can see two identical LacI proteins bound to each other and to the lacO promoter. This tutorial will highlight some of this repressor's structure and thus function. You can click and drag to see the shape before clicking on the buttons below.

Convert the proteins to cartoon shape and zoom in on the portions that allow the two LacI monomers to hold on to each other to make the homodimer. What secondary structure reaches out to the other LacI protein? In which DNA groove do the LacI proteins bind the lacO promoter?

Hide the LacI protein and look at the DNA's shape that is affected by LacI binding. Is the DNA still a straight molecule? What shape change can you see?

Zoom in on the portion of the double helix that has a kink in it that causes the bend. After a while, the protein will come back into view. Can you see why the DNA bends at this precise location?

You can zoom in to see which bases are located at the kink site by converting them to CPK colors and spacefill model. You can even tell that this base pair is a G:C base pair because of the three sites of H-bonding.

Genomics

Biology Home Page