Conformational studies of mitochondrial DNA

Ring DNA from rat liver mitochondria has been examined by circular dichroism (CD) in the region of the 225 to 320 m/~ and the followings have been clarified. The ring DNA gives a CD spectral curve somewhat different from linear DNA from nuclei, showing a big positive peak at 266 m/~ and a small negative band at 243 m!~. That is, the positive CD band of ring DNA shifted by about 7 m/~ to the shorter wavelength side from the band of the ordinary nuclear DNA, 273 m!~. Negative band appeared at the same region as that of linear DNA but reduced in depth. Heat denaturation of the ring DNA induced a red shift of the positive band, by about 4 mp., but no change in negative band. From these experimental results it has been concluded that the ring DNA has highly twisted conformation and high in G.C contents, both of which are responsible for the blue shift of the CD spectrum.