Repair-Independent Chromatin Assembly onto Active Ribosomal Genes in Yeast after UV Irradiation

Abstract

Chromatin rearrangements occur during repair of cyclobutane pyrimidine dimers (CPDs) by nucleotide excision repair (NER). Thereafter, the original structure must be restored to retain normal genomic functions. How NER proceeds through nonnucleosomal chromatin and how open chromatin is reestablished after repair are unknown. We analyzed NER in ribosomal genes (rDNA), which are present in multiple copies but only a fraction are actively transcribed and nonnucleosomal. We show that removal of CPDs is fast in the active rDNA and that chromatin reorganization occurs during NER. Furthermore, chromatin assembles on nonnucleosomal rDNA during the early events of NER but in the absence of DNA repair. The resumption of transcription after removal of CPDs correlates with the reappearance of nonnucleosomal chromatin. To date, only the passage of replication machinery was thought to package ribosomal genes in nucleosomes. In this report, we show that early events after formation of UV photoproducts in DNA also promote chromatin assembly.

ACKNOWLEDGMENTS

We are grateful to L. Gaudreau and B. Leblanc at the Université de Sherbrooke for critical reading of the manuscript and to M. Tremblay for technical help.

The majority of this work was supported by a grant from the Canadian Institutes of Health Research (CIHR) to A.C. D.F. and V.B. were supported by National Institutes of Health grants ES02614 and ES04106 from the National Institute of Environmental Health Sciences (NIEHS) to M.J.S.

The contents of this study are solely the responsibility of the authors and do not represent the official views of the NIEHS.