A cesium chloride gradient of total DNA isolated from yeast cells containing a rho- deletion mutant in its mitochondrial genome. Mitochondrial DNA in yeast is approximately 80% A/T base pairs, which makes it significantly less dense than chromosomal DNA. The photograph shows Hoechst 33258 (bis-benzimide) stained total yeast DNA run in a Sorval Discovery 90SE Ultracentrifuge for 20 hours at 55,000 rpms.  The DNA is fluorescing in the presence of UV light.  The bright  band 2/3 down the tube is the chromosomal DNA, the loghter band right underneath it is ribosomal DNA which has a higher G/C content.  The light band in the center of the tube is mitochondrial DNA.