Affiliation:
1. Cell Biology and Genetics Program, Sloan-Kettering Institute and Cornell University Graduate School of Medical Sciences, New York, New York 10021, USA.
Abstract
Genetic instability is promoted by unusual sequence arrangements and DNA structures. Hairpin DNA structures can form from palindromes and from triplet repeats, and they are also intermediates in V(D)J recombination. We have measured the genetic stability of a large palindrome which has the potential to form a one-stranded hairpin or a two-stranded cruciform structure and have analyzed recombinants at the molecular level. A palindrome of 15.3 kb introduced as a transgene was found to be transmitted at a normal Mendelian ratio in mice, in striking contrast to the profound instability of large palindromes in prokaryotic systems. In a significant number of progeny mice, however, the palindromic transgene is rearranged; between 15 and 56% of progeny contain rearrangements. Rearrangements within the palindromic repeat occur both by illegitimate and homologous, reciprocal recombination. Gene conversion within the transgene locus, as quantitated by a novel sperm fluorescence assay, is also elevated. Illegitimate events often take the form of an asymmetric deletion that eliminates the central symmetry of the palindrome. Such asymmetric transgene deletions, including those that maintain one complete half of the palindromic repeat, are stabilized so that they cannot undergo further illegitimate rearrangements, and they also exhibit reduced levels of gene conversion. By contrast, transgene rearrangements that maintain the central symmetry continue to be unstable. Based on the observed events, we propose that one mechanism promoting the instability of the palindrome may involve breaks generated at the hairpin structure by a hairpin-nicking activity, as previously detected in somatic cells. Because mammalian cells are capable of efficiently repairing chromosome breaks through nonhomologous processes, the resealing of such breaks introduces a stabilizing asymmetry at the center of the palindrome. We propose that the ability of mammalian cells to eliminate the perfect symmetry in a palindromic sequence may be an important DNA repair pathway, with implications regarding the metabolism of palindromic repeats, the mutability of quasipalindromic triplet repeats, and the early steps in gene amplification events.
Publisher
American Society for Microbiology
Subject
Cell Biology,Molecular Biology
Reference51 articles.
1. Trinucleotide repeat expansion and human disease. Annu;Ashley C. T.;Rev. Genet.,1995
2. Ausubel F. M. R. Brent R. E. Kingston D. D. Moore J. G. Seidman J. A. Smith K. Struhl L. M. Albright D. M. Coen and A. Varki. 1995. Current protocols in molecular biology. John Wiley & Sons Inc. New York N.Y.
3. Somatic expression of herpes thymidine kinase in mice following injection of a fusion gene into eggs;Brinster R. L.;Cell,1981
4. Copy-choice recombination mediated by DNA polymerase III holoenzyme from Escherichia coli;Canceill D.;Proc. Natl. Acad. Sci. USA,1996
5. Hairpins are formed by the single DNA strands of the fragile X triplet repeats: structure and biological implications;Chen X.;Proc. Natl. Acad. Sci. USA,1995
Cited by
152 articles.
订阅此论文施引文献
订阅此论文施引文献,注册后可以免费订阅5篇论文的施引文献,订阅后可以查看论文全部施引文献