DNA, isolated from a strain of Rhodopseudomonas spheroides, showed two components when banded in CsCl, with buoyant densities of 1.719 and 1.724 g/ml. The lighter band comprised about 8% of the total. Using a mild lysis procedure, it was possible to extract DNA of which 15-20% was circular. Circular DNA, isolated by dye-buoyant density centrifugation, contained two components with buoyant densities 1.718 and 1.724 g/ml. Sedimentation of the circular DNA gave two peaks, with S20,w values of 78.2S and 52.7S; sedimentation in alkali, and in neutral solution after denaturation, showed that the first peak was closed circular and the second peak open circular DNA. Band-buoyant density sedimentation of the circular DNA in alkaline CsCl initially showed two peaks; after a time, each peak split into two. The alkaline buoyant densities of the four peaks were consistent with open and closed circles with neutral buoyant densities 1.718 and 1.724 g/ml. It is concluded that Rps. spheroides contains two circular satellite DNA species, with the same molecular weight of 70-75 × 106 daltons, but with slightly different base compositions.
All Science Journal Classification (ASJC) codes
- Molecular Biology