This Article Full Text (PDF) Alert me when this article is cited Alert me if a correction is posted Services Similar articles in this journal Similar articles in PubMed Alert me to new issues of the journal Download to citation manager Reprints and Permissions Copyright Information Books from ASM Press MicrobeWorld Citing Articles Citing Articles via HighWire Citing Articles via Google Scholar Google Scholar Articles by Leu, T H Articles by Hamlin, J L Search for Related Content PubMed PubMed Citation Articles by Leu, T H Articles by Hamlin, J L

 Previous Article  |  Next Article 

Mol Cell Biol. 1992 June; 12(6): 2804-2812

Activation of a mammalian origin of replication by chromosomal rearrangement.

Department of Biochemistry, University of Virginia School of Medicine, Charlottesville 22908.

ABSTRACT

The methotrexate-resistant Chinese hamster cell line DC3F/A3-4K (A3/4K) contains at least two prominent dihydrofolate reductase amplicon types. The type I amplicons, constituting approximately 80% of the total, are at least 650 kb in length, but the endpoints have not yet been characterized. The type II sequences represent approximately 20% of amplicons, are 450 kb in length, and are arranged as alternating head-to-head and tail-to-tail repeats. In previous studies on the CHOC 400 line, in which the amplicons are much smaller, a replication initiation locus (ori-beta/ori-gamma) has been shown to reside downstream from the dihydrofolate reductase gene. In a more recent study on the larger amplicons of A3/4K cells, we detected an additional initiation locus (ori-alpha) lying approximately 240 kb upstream from ori-beta/ori-gamma. Interestingly, in vivo labelling experiments suggested that replication forks diverge from ori-alpha only in the downstream direction. This finding suggested either that ori-alpha is a unidirectional origin or that a terminus lies immediately upstream from ori-alpha. However, in this study, we show that ori-alpha is actually very close to the head-to-head palindromic junction sequence between the minor type II amplicons in A3/4K cells; furthermore, ori-alpha is active in the early S period in the type II amplicons but not in the larger type I sequences that lack this palindromic junction. This is the first direct demonstration in mammalian cells that a cryptic origin can be activated by chromosomal rearrangement, presumably by deleting negative regulatory elements or by creating a more favorable chromosomal milieu for initiation.

This article has been cited by other articles:

• Altman, A. L., Fanning, E. (2001). The Chinese Hamster Dihydrofolate Reductase Replication Origin Beta Is Active at Multiple Ectopic Chromosomal Locations and Requires Specific DNA Sequence Elements for Activity. Mol. Cell. Biol. 21: 1098-1110 [Abstract] [Full Text]  
• Hickman, M. J., Samson, L. D. (1999). Role of DNA mismatch repair and p53 in signaling induction of apoptosis by alkylating agents. Proc. Natl. Acad. Sci. USA 96: 10764-10769 [Abstract] [Full Text]