Mammalian recombination hot spot in a DNA loop anchorage region: A model for the study of common fragile sites

✍ Scribed by E. Yu. Svetlova; S.V. Razin; M. Debatisse

• Publisher: John Wiley and Sons
• Year: 2001
• Tongue: English
• Weight: 156 KB
• Volume: 81
• Category: Article
• ISSN: 0730-2312
• DOI: 10.1002/jcb.1081

✦ Synopsis

We analyzed the replication pattern and the topological organization of a 200 kb long Chinese hamster polygenic locus, which spans the boundary of two isochores. One of them is G C rich while the second one is highly A T rich. Previous analysis of mutants ampli®ed for this locus had identi®ed, within the A T rich isochore, a mitotic recombination hotspot and a replication origin separated by some 7 kb. The recombination hotspot exhibits structural features repeatedly observed at common fragile sites, including a typical enrichment in peaks of enhanced DNA helix ¯exibility. By studying the replication pattern of the same locus in the non-ampli®ed CHO cells, we con®rm here the localization of the replication origin and show that the mitotic recombination hotspot does not correspond to a replicon junction. This ®nding makes questionable current hypotheses correlating replication termination regions with recombination prone sequences. Using topoisomerase II-mediated DNA cleavage at matrix attachment sites, we identi®ed a 40 kb-long DNA anchorage region extending all along a transcription unit nested within the A T rich isochore. Both the recombination hotspot and the replication origin lie within this topoisomerase II sensitive region, which suggests that features essential for initiation of recombination and initiation of DNA replication cluster within DNA anchorage regions. Features common to this region and to common fragile sites are discussed.