Electron micrsocopic analysis of DNA replication in eukaryotes

An electron microscopic analysis of replication intermediates in chromosomal DNA from several systems has been made. In all of them, besides entirely double stranded molecules, only molecules with clustered small "eyes" and partially or entirely single stranded molecules were observed. Early cleavage embryos of D. melanogaster alone showed the presence also of molecules with long replication "eyes". These patterns strongly support a unifying interpretation we recently proposed for chromosomal DNA replication in eukaryotes. As for the replication of specific chromosomal genes, a more refined approach has led us to envisage the rRNA gene cluster in X. laevis as a multi-replicon complex, the origins of replication being confined to the non-transcribed spacers.