Sites of topoisomerase I action on X. laevis ribosomal chromatin: Transcriptionally active rDNA has an ∼200 bp repeating structure

Valeria Culotta, Barbara Sollner-Webb

Research output: Contribution to journalArticlepeer-review

Abstract

The sites at which topoisomerase I interacts with the transcriptionally active ribosomal chromatin of Xenopus oocytes were mapped by treating oocyte nuclei first with camptothecin to stabilize topoisomerase I-rDNA reaction intermediates, and then with SDS to resolve these adducts as protein-linked nicks in the DNA. Strikingly, the topoisomerase I sites are concentrated in the region encoding the 18S, 5.8S, and 28S rRNAs, where they are spaced with a periodicity of ∼200 nucleotides. Plasmid rDNA that has assembled into a nucleoprotein structure in an oocyte nuclear extract yields this same restricted pattern of sites, while rDNA that is not in a chromatin structure exhibits a continuum of topoisomerase I cleavages. Thus, the ∼200 bp spacing of sites of topoisomerase I interaction evidently reflects rDNA chromatin structure. These results indicate that the active rRNA genes are organized into nucleosome-like arrays, with topoisomerase I located in the linker regions.

Original languageEnglish (US)
Pages (from-to)585-597
Number of pages13
JournalCell
Volume52
Issue number4
DOIs
StatePublished - Feb 26 1988

ASJC Scopus subject areas

  • Biochemistry, Genetics and Molecular Biology(all)

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