A study of sequence homologies in four satellite DNAs of man

Abstract

Satellites I, II, III and IV (Corneo et al., 1968,1970,1971) have been purified from human male placental DNA. The sequences present in these four DNA components have been characterized by analytical buoyant density, thermal denaturation, DNA reassociation, DNA hybridization and gel electrophoresis coupled with hybridization following either HaeIII or EcoRI restriction endonuclease digestion. Satellites III and IV were found to be virtually indistinguishable by a variety of criteria. Cross-satellite reassociation showed that 40% of the molecules present in satellite III contain sequences that are homologous to 10% of the molecules of either satellite I or satellite II. Reassociated satellite I melts as a single component, as do the hybrid duplexes between satellite I and satellite III. In contrast, reassociated satellites II, III and IV, and the hybrid duplexes formed between satellites II and III and between satellites II and IV, melt as two distinct components with different thermal stabilities. Digestion of satellite III with HaeIII gives rise to a series of fragments whose sizes are 2, 3, 4, 5, 6, 7, 8 and 11 times the size of the smallest 0.17 × 10 3 basepair fragment, in addition to a 3.4 × 10 3 base-pair male-specific fragment (Cooke, 1976) and high molecular weight material. The sequences contained in the fragments of the HaeIII ladder are diverged from each other as well as being non-homologous with those of the 3.4 × 10 3 base-pair and high molecular weight fragments. The latter contain EcoRI recognition sites. Satellite II has a similar pattern of fragments to satellite III following digestion with HaeIII, although it can be distinguished from satellite III on the basis of the products of EcoRI digestion. Satellite I contains neither HaeIII nor EcoRI recognition sites. The cross-satellite homologies of the sequences present in fragments of differing sizes produced by restriction enzyme digestion have also been studied.