The dichroism of DNA in electric fields

Abstract

Abstract We have studied the dichroism of various samples of calf thymus DNA (of molecular weight from 3 × 10 5 to 7 × 10 6 ) in pulsed electric fields. The results may be summarized as follows: We find that calf thymus DNA behaves in electrical orientation as if it possessed a large permanent dipole moment. This apparent moment is sensitive to such effects as Mg ++ binding which lower the net charge on DNA. The limiting dichroism at infinite field corresponds to an angle of at least 80% between the transition moments at 265 nm and the helix axis, and could be consistant with a number of known forms of DNA. This result is independent of DNA molecular weight. There is evidence that the conformation may be different in 80% ethanol. The dichroism relaxation curves contain a component with a relaxation time of about 8 μsec, which is nearly independent of molecular weight, and a longest component which behaves either according to the Broersma theory for low‐molecular‐weight samples, or the Zimm‐Rouse theory at high molecular weights.