Different satellite deoxyribonucleic acids of guinea pig and ox

By Ag+-Cs2SO4 preparative centrifugation two new satellite DNAs, called satellite DNAs II and III, are isolated from guinea pig DNA, besides satellite DNA I which was previously isolated. Guinea pig satellite DNAs II and III have the same density of 1.704 g/cm3 in caesium chloride: they each account for approximately 2.5% of the total DNA and appear as distinct bands on the light side of the Ag+-Cs2SO4 gradient. Their complementary strands differ in density one from the other in alkaline caesium chloride, respectively, by 0.031 and 0.022 g per cm3. They also differ in density in neutral caesium chloride. The two satellite DNAs previously isolated from calf thymus can be separated into their complementary strands. The two strands of calf thymus satellite DNA I (d 1.713 g/cm3) differ in density in alkaline caesium chloride by 0.019 g/cm3: those of calf thymus satellite DNA II differ by only 0.005 g/cm3. The kinetics of renaturation of the three guinea pig satellite DNAs and of calf thymus satellite DNA I were studied by determining the optical reassociation curves. On the basis of these results the repeated unit of guinea pig satellite DNA I would appear to be considerably longer than those of the other satellite DNAs.