Generation of specific repeated fragments of eukaryote DNA

Calf-thymus DNA, hydrolyzed with a site-specific endonuclease from Haemophilus influenzae Rd, yields 12 discrete bands on polyacrylamide-agarose gels. These range in size from 7.5 x 10(4) to 2 x 10(6) daltons, and they represent about 5% of the total DNA with individual fragments comprising 0.1-1.5%. The various DNA segments are repeated between 1500 and 220,000 times per haploid genome. Whereas the wide range of reiteration frequencies suggests different origins for some of the fragments, the bias in fragment densities in CsCl and in Ag(+)-Cs(2)SO(4) toward those of known satellite DNAs suggests similar origins for some of them. Models for the possible origin of the DNA fragments can be grouped into three distinct, experimentally distinguishable, classes.