Twelve clones of monkey DNA obtained by a procedure that enriches 103-to 104-fold for nascent sequences activated early in S phase (G. Kaufmann, M. Zannis-Hadjopoulos, and R. G. Martin, Mol. Cell. Biol. 5:721-727, 1985) have been examined. Only 2 of the 12 ors sequences (origin-enriched sequences) are unique (orsl and ors8). Three contain the highly reiterated Alu family (ors3, ors9, and orsll). One contains the highly reiterated a-satellite family (orsl2), but none contain the Kpn family. Those remaining contain middle repetitive sequences. Two examples of the same middle repetitive sequence were found (ors2 and ors6). Three of the middle repetitive sequences (the ors2-ors6 pair, orsS, and orslO) are moderately dispersed; one (ors4) is highly dispersed. The last, ors7, has been mapped to the bona fide replication origin of the D loop of mitochondrial DNA. Of the nine ors sequences tested, half possess snapback (intrachain reannealing) properties.Very little is known of the structural features of nuclear mammalian origins of replication. If DNA synthesis is precisely programmed (12,15), then one might expect some common feature(s) of structure or sequence among those origins activated at each point in S phase (3,5,13,29). Indeed, Radford et al. (27) observed an accumulation of repetitive sequences after release from a hydroxyurea block and therefore suggested that origin regions might be enriched for dispersed repetitive sequences. Gronostajski et al. (16a) have purified a cellular protein required for the initiation of adenovirus DNA replication, nuclear factor I, and have shown that HeLa cell sequences can be isolated that preferentially bind to this protein. They have proposed that these sequences might represent HeLa replication origins. On the other hand, it has been observed (41) that short nascent DNA strands are enriched for snapback sequences and has been suggested therefore that origins may be enriched for inverted repeats. Finally, Roth et al. (30) and Montiel et al. (25) have shown that a number of mouse and human DNA sequences, respectively, contain AT-rich regions homologous to the presumptive nuclear replication origins of yeast (ars sequences) and can serve as replication origins for yeast plasmids. They have proposed that these sequences may be mouse and human DNA replication origins.Unlike the situation in mammalian cells, considerable progress toward the characterization of replication origins has been made for Saccharomyces cerevisiae. The ars sequences have been isolated on the basis of their ability to serve as origins for plasmid replication (7,33,34). Curiously, the yeast mitochondrial replication origin also serves as an ars element (18). Both repetitive and unique nuclear ars sequences have been found (8,9,22 tandemly repeated at the telomeres of yeast chromosomes (8,9). The relevance of these findings to mammalian origins is unknown.In mammalian cells, mitochondrial DNA (mtDNA) is known to commence replication at a few closely linked sites with the L strand as the template. Most...
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.
hi@scite.ai
10624 S. Eastern Ave., Ste. A-614
Henderson, NV 89052, USA
Copyright © 2024 scite LLC. All rights reserved.
Made with 💙 for researchers
Part of the Research Solutions Family.