Psoralen photocrosslinking, a tool to study the chromatin structure of RNA polymerase I--transcribed ribosomal genes

Biochem Cell Biol. 2005 Aug;83(4):449-59. doi: 10.1139/o05-141.


The chromatin structure of RNA polymerase I--transcribed ribosomal DNA (rDNA) is well characterized. In most organisms, i.e., lower eukaryotes, plants, and animals, only a fraction of ribosomal genes are transcriptionally active. At the chromatin level inactive rDNA is assembled into arrays of nucleosomes, whereas transcriptionally active rDNA does not contain canonical nucleosomes. To separate inactive (nucleosomal) and active (non-nucleosomal) rDNA, the technique of psoralen photocrosslinking has been used successfully both in vitro and in vivo. In Saccharomyces cerevisiae, the structure of rDNA chromatin has been particularly well studied during transcription and during DNA replication. Thus, the yeast rDNA locus has become a good model system to study the interplay of all nuclear DNA processes and chromatin. In this review we focused on the studies of chromatin in ribosomal genes and how these results have helped to address the fundamental question: What is the structure of chromatin in the coding regions of genes?

Publication types

  • Research Support, Non-U.S. Gov't
  • Review

MeSH terms

  • Chromatin* / chemistry
  • Chromatin* / genetics
  • Chromatin* / radiation effects
  • Cross-Linking Reagents
  • DNA Repair / genetics*
  • DNA, Fungal / genetics
  • DNA, Ribosomal / genetics
  • Genes, Fungal*
  • Photosensitizing Agents / pharmacology*
  • RNA Polymerase I / genetics*
  • Saccharomyces cerevisiae / genetics*
  • Saccharomyces cerevisiae / metabolism*
  • Saccharomyces cerevisiae / radiation effects
  • Transcription, Genetic
  • Trioxsalen / pharmacology*
  • Ultraviolet Rays


  • Chromatin
  • Cross-Linking Reagents
  • DNA, Fungal
  • DNA, Ribosomal
  • Photosensitizing Agents
  • RNA Polymerase I
  • Trioxsalen