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Central to the development and survival of all organisms is the regulation of gene expression, which begins with the process of transcription catalyzed by RNA polymerases. During transcription of protein-coding genes, the general transcription factors (GTFs) work alongside RNA polymerase II (Pol II) to assemble the preinitiation complex at the transcription start site, open the promoter DNA, initiate synthesis of the nascent messenger RNA, transition to productive elongation, and ultimately terminate transcription. Through these different stages of transcription, Pol II is dynamically phosphorylated at the C-terminal tail of its largest subunit, serving as a control mechanism for Pol II elongation and a signaling/binding platform for co-transcriptional factors. The large number of core protein factors participating in the fundamental steps of transcription add dense layers of regulation that contribute to the complexity of temporal and spatial control of gene expression within any given cell type. The Pol II transcription system is highly conserved across different levels of eukaryotes; however, most of the information here will focus on the human Pol II system. This review walks through various stages of transcription, from preinitiation complex assembly to termination, highlighting the functions and mechanisms of the core machinery that participates in each stage.
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This content will become publicly available on June 1, 2026
Genetic Factors Linking Nucleolar Stress with R2 Retrotransposon Expression in Drosophila melanogaster
R2 retrotransposons reside exclusively within the 28S regions of 10–20% of all rDNA genes comprising the nucleolar organizer loci on the X and Y chromosomes of Drosophila melanogaster. These R2-inserted genes are normally silent and heterochromatic. When expressed, however, the R2 transcript is co-transcribed with the 28S rRNA. Self-cleavage releases a 3.6 kb mature R2 transcript that encodes a single protein with endonuclease and reverse transcriptase activities that facilitate R2 element transposition by target-primed reverse transcription. While we know the molecular details of R2 transposition, we know little about the genetic mechanisms that initiate R2 transcription. Here, we examine R2 expression in wild type versus mutant backgrounds. R2 expression in stage 1–4 wild type egg chambers was variable depending on the stock. R2 expression was silent in wild type stages 5–10 but was consistently active during nurse cell nuclear breakdown in stages 12–13 regardless of the genetic background. Massive R2 expression occurred in stages 5–10 upon loss of Udd, an RNA Pol I transcription factor. Similarly, loss of Nopp140, an early ribosome assembly factor, induced R2 expression more so in somatic tissues. Interestingly, over-expression of the Nopp140-RGG isoform but not the Nopp140-True isoform induced R2 expression in larval somatic tissues, suggesting Nopp140-RGG could potentially affect rDNA chromatin structure. Conversely, Minute mutations in genes encoding ribosomal proteins had minor positive effects on R2 expression. We conclude that R2 expression is largely controlled by factors regulating RNA Pol I transcription and early ribosome assembly.
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- PAR ID:
- 10657766
- Publisher / Repository:
- International Journal of Molecular Sciences
- Date Published:
- Journal Name:
- International Journal of Molecular Sciences
- Volume:
- 26
- Issue:
- 12
- ISSN:
- 1422-0067
- Page Range / eLocation ID:
- 5480
- Subject(s) / Keyword(s):
- R2 retrotransposon Drosophila Nopp140 nucleolar stress rDNA nucleolus
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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