Dynamics of long DNA confined by linear polymers.

We studied the electrophoretic behavior of long DNA molecules in a linear polymer [polyacrylamide (PA)] solution through direct observation by means of fluorescence microscopy. DNA migrates in an I-shaped conformation in concentrated polymer solutions under steady electric fields, but it is not stretched up to its natural contour length in this I-shaped conformation under such fields. The stretching of DNA is induced under alternating current fields through the entanglement effect between DNA and host polymers. We experimentally investigated the conditions required for this stretching phenomenon and found that DNA can be stretched at a concentration of around 7% PA, under a field of around 10 Hz. These conditions do not depend on the length of the DNA chains. It is expected that DNA stretching will be useful in the optical mapping of specific sites along an individual DNA chain.