Role for DNA replication in beta-globin gene activation.

Transcriptional activation of the Xenopus laevis beta-globin gene requires the synergistic action of the simian virus 40 enhancer and DNA replication in DEAE-dextran-mediated HeLa cell transfections. Replication does not act through covalent modification of the template, since its requirement was not obviated by the prior replication of the transfected DNA in eucaryotic cells. Transfection of DNA over a 100-fold range demonstrates that replication does not contribute to gene activation simply increasing template copy number. Furthermore, in cotransfections of replicating and nonreplicating constructs, only replicating templates were transcribed. Replication is not simply a requirement of chromatin assembly, since even unreplicated templates generated nucleosomal ladders. Stimulation of beta-globin transcription by DNA replication, though less marked, was also observed in calcium phosphate transfections. We interpret these results as revealing a dynamic role for replication in gene activation.