The coordinate replication of the human beta-globin gene domain reflects its transcriptional activity and nuclease hypersensitivity.

The temporal order of replication of DNA sequences in the chromosomal domain containing the human beta-globin gene cluster and its flanking sequences (140 kilobases) was measured and compared in two different human cell lines. In human erythroleukemia (K562) cells, in which embryonic and fetal globin genes are transcribed, all of the sequences we examined from the beta-globin domain replicated early during S phase, while in HeLa cells, in which globin genes are transcriptionally silent, these sequences replicated late during S. Potential sites of initiation of DNA replication within this domain were identified. The beta-globin gene domain was also found to differ with respect to the nuclease sensitivity of the chromatin in these two cell lines. In K562 cells, hypersensitive sites for endogenous nucleases and DNase I were present in the chromatin near the earliest-replicating segments in the beta-globin domain.