Attempts at identifying DNA replication origins in human cells have been performed with a variety of molecular genetic and biochemical approaches, with often controversial results. The combination of bromodeoxyuridine labelling, immunopurification of newly synthesized labelled DNA, measurement of the relative abundance of markers in this DNA by quantitative competitive PCR, has allowed the identification within 450 bp of the start-site of DNA replication located at the human lamin B2 gene. The origin is located near the non-transcribed spacer between two highly transcribed genes and shows evidence of a number of specific protein-DNA interactions, the most prominent of which disappears when the cells are differentiated into a non-proliferating state.
