DNA Looping and Gene Expression

We know so much, and then again we know so little. Crick and Watson discovered the structure of DNA in 1953 and it ushered in a revolution in biotechnology and genetics. But despite the many incredible and audacious advances in our knowledge since then the DNA molecule still holds many mysteries, and one of those is DNA looping.

However, science is not completely in the dark about DNA looping.

DNA looping is exactly that - the DNA molecule actually forms loops. These loops are created by proteins and protein complexes binding to different regions of the DNA structure. The proteins interact with each other and this causes loops to form. DNA looping is involved in many cellular processes such as transcription, recombination, gene expression, and replication. The neat thing about DNA looping is that when loops form in the DNA structure proteins that are bound some distance away from the genes they control can be brought to the promoter region by looping the intervening DNA (Leonor Saiz and Jose MG Vilar: DNA Looping: The Consequences and its Control. Current Opinion in Structural Biology 2006, 16: 344-350).

There are two different types of DNA looping. The classification comes from the physical forces that control their formation:

1) Short or energetic - for DNA ~150 bp elasticity is the dominant force, and the bending and twisting of DNA is important, as is the elastic properties of the molecules that tie the loop.

2) Long or entropic - what is key is the motion of the DNA regions in the cell before they find each other.

DNA looping plays many important roles in the life of a cell. By bringing two DNA regions together DNA loops enable the transfer of genetic information during recombination; they also tie the ends of chromosomes, and regulate the length of telomeres.

It is therefore a safe bet to assume that many malfunctions that occur in our bodies will be down to faults in the DNA looping process. So the more that is known about how DNA loops make sure gene expression goes off without a hitch, and the right gene is turned on - the better our chances of being able to fix things when they go wrong.

Understanding DNA looping is a burgeoning research endeavour, especially as some diseases, including cancers are caused or made worse by incorrect looping and errors in gene expression.