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Updated: Jul 19, 2026

Structure-function Studies in Mouse Embryonic Stem Cells Using Recombinase-mediated Cassette Exchange
Published on: April 27, 2017
Discrete functional elements required for initiation activity of the Chinese hamster dihydrofolate reductase origin
Steven J Gray1, Guoqi Liu, Amy L Altman
1Department of Biological Sciences, Vanderbilt-Ingram Cancer Center, Vanderbilt University, Nashville, TN 37235-1634, USA.
Abstract:
The Chinese hamster dihydrofolate reductase (DHFR) DNA replication initiation region, the 5.8 kb ori-beta, can function as a DNA replicator at random ectopic chromosomal sites in hamster cells. We report a detailed genetic analysis of the DiNucleotide Repeat (DNR) element, one of several sequence elements necessary for ectopic ori-beta activity. Deletions within ori-beta identified a 132 bp core region within the DNR element, consisting mainly of dinucleotide repeats, and a downstream region that are required for ori-beta initiation activity at non-specific ectopic sites in hamster cells. Replacement of the DNR element with Xenopus or mouse transcriptional elements from rDNA genes restored full levels of initiation activity, but replacement with a nucleosome positioning element or a viral intron sequence did not. The requirement for the DNR element and three other ori-beta sequence elements was conserved when ori-beta activity was tested at either random sites or at a single specific ectopic chromosomal site in human cells. These results confirm the importance of specific cis-acting elements in directing the initiation of DNA replication in mammalian cells, and provide new evidence that transcriptional elements can functionally substitute for one of these elements in ori-beta.
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