The DNA fraction enriched in replication origins was isolated from chicken erythroblastosis cells with the aid of nascent DNA strand extrusion method. In renaturation experiments, the sequence specificity of this DNA fraction (oriDNA) was compared to the sequence specificity of the nuclear matrix DNA. The oriDNA was shown to comprise a specific subset of unique genes all of which being represented also in the nuclear matrix DNA. The same unique DNA sequences were found to be depleted from the oriDNA and from the nuclear matrix DNA. A conclusion has been drawn that replication origins are located at the basements of DNA loops. The putative positions of replication origins within the domain of chicken alpha globin genes were mapped by hybridization experiments and were found to coincide with the positions of stable (not depending on the transcriptional state of globin genes) sites of DNA attachment to the nuclear skeleton.