This Article Full Text (PDF) Other Versions of this Article: MCB.01409-06v1 26/23/8781    most recent Alert me when this article is cited Alert me if a correction is posted Services Similar articles in this journal Similar articles in PubMed Alert me to new issues of the journal Download to citation manager Reprints and Permissions Copyright Information Books from ASM Press MicrobeWorld Citing Articles Citing Articles via HighWire Citing Articles via Google Scholar Google Scholar Articles by Ye, J. Articles by Eickbush, T. H. Search for Related Content PubMed PubMed Citation Articles by Ye, J. Articles by Eickbush, T. H.

 Previous Article  |  Next Article 

Mol. Cell. Biol. doi:10.1128/MCB.01409-06
Copyright (c) 2006, American Society for Microbiology and/or the Listed Authors/Institutions. All Rights Reserved.

Chromatin structure and transcription of the R1 and R2 inserted ribosomal RNA genes of Drosophila melanogaster

University of Rochester, Department of Biology, Rochester, New York 14627

^* To whom correspondence should be addressed. Email: eick{at}mail.rochester.edu.

	Abstract

About half of the ribosomal RNA gene units (rDNA units) of Drosophila melanogaster are inserted by the retrotransposable elements R1 and R2. Because transcripts to R1 and R2 were difficult to detect on blots, and electron microscopic observations of rRNA synthesis suggested only uninserted rDNA units were transcribed, it has long been postulated that inserted rDNA units are in a repressed (inactive) chromatin structure. Studies described here suggest that inserted and uninserted units are equally accessible to DNase I and micrococcal nuclease, and contain similar levels of histone H3 and H4 acetylation and H3K9 methylation. These studies have low sensitivity because psoralen cross-linking suggested few (est. <10%) of the rDNA units of any type are transcriptionally active. Nuclear run-on experiments revealed that R1-inserted and R2-inserted units are activated for transcription at about one-fifth and one-tenth, respectively, the rate of uninserted units. Most transcription complexes of the inserted units terminate within the elements, thus explaining why previous molecular and electron microscopic methods indicated inserted units are seldom transcribed. The accumulating data suggests that all units within small regions of the rDNA loci are activated for transcription with most control over R1 and R2 activity involving steps downstream of transcription initiation.

This article has been cited by other articles:

• Eickbush, D. G., Ye, J., Zhang, X., Burke, W. D., Eickbush, T. H. (2008). Epigenetic Regulation of Retrotransposons within the Nucleolus of Drosophila. Mol. Cell. Biol. 28: 6452-6461 [Abstract] [Full Text]