Sequence and context effects on origin function in mammalian cells.
Jacob and Brenner proposed a model for control of DNA replication in which a trans-acting initiator protein binds to a cis-acting replicator to effect initiation of nascent DNA chains at a fixed locus. Although replicators have been identified in prokaryotic and simple eukaryotic genomes, it has been much more difficult to demonstrate their presence in mammalian chromosomes. Owing to the lack of genetic approaches for identifying mammalian replicators, investigators have directed attention to localizing nascent strand start sites, which should lie close to replicators. Toward this end, a variety of clever techniques have been invented for analyzing replication intermediates, but only rarely have more than one of these techniques been applied to a single locus. However, virtually all have been used to analyze the dihydrofolate reductase locus in CHO cells. The picture that has developed in this locus is that initiation can occur at any of a large number of sites scattered throughout a broad zone, but somewhat more frequently near two sites that may correspond to true genetic replicators. Furthermore, it appears that local transcriptional activity, as well as appropriate torsional stress (as imparted by local attachment to the nuclear matrix), may have profound effects on origin activity.
Dijkwel
P A
PA
Department of Biochemistry, University of Virginia School of Medicine, Charlottesville 22908, USA.
Hamlin
J L
JL
D000818:Animals; D016466:CHO Cells; D006224:Cricetinae; D004261:DNA Replication / Q000235:genetics*; D008322:Mammals / Q000235:genetics*; D008957:Models, Genetic; D018741:Replication Origin / Q000235:genetics*; D013762:Tetrahydrofolate Dehydrogenase / Q000235:genetics
D013762:Tetrahydrofolate Dehydrogenase