Coliphage 186 genetic switch: a single molecule study

It is increasingly clear that in most cases genes are regulated by wrapping or looping of DNA on large, cooperatively assembled protein complexes. In most eukaryotic organisms, 150 bp of DNA are wrapped twice around histone octamers (nucleosomes). Furthermore, interaction between proteins bound at distant sites on the DNA may cause looping out of the intervening DNA with regulatory significance. The mechanism by which these DNA- protein nanostructures are formed is not clear. It is tantalizing how little information is available about the energetics, kinetics and equilibrium between DNA wrapping and looping given the crucial role they play on gene regulation and DNA physiology. The interaction between the bacteriophage repressor 186CI and its DNA is an ideal model system to study DNA wrapping and looping and to reveal fundamental principles of long-range interactions and regulation by nucleoprotein complexes. Here we report on AFM work aimed at elucidating the 186CI-DNA interaction.