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Mol Cell. 2016 Apr 21;62(2):237-247. doi: 10.1016/j.molcel.2016.03.007. Epub 2016 Apr 7.

Enhancer Regulation of Transcriptional Bursting Parameters Revealed by Forced Chromatin Looping.

Author information

1
Division of Hematology, Children's Hospital of Pennsylvania, Philadelphia, PA 19104, USA; Perelman School of Medicine, University of Pennsylvania, Philadelphia, PA 19104, USA.
2
Department of Bioengineering, University of Pennsylvania, Philadelphia, PA 19104, USA. Electronic address: arjunrajlab@gmail.com.
3
Division of Hematology, Children's Hospital of Pennsylvania, Philadelphia, PA 19104, USA; Perelman School of Medicine, University of Pennsylvania, Philadelphia, PA 19104, USA. Electronic address: blobel@email.chop.edu.

Abstract

Mammalian genes transcribe RNA not continuously, but in bursts. Transcriptional output can be modulated by altering burst fraction or burst size, but how regulatory elements control bursting parameters remains unclear. Single-molecule RNA FISH experiments revealed that the β-globin enhancer (LCR) predominantly augments transcriptional burst fraction of the β-globin gene with modest stimulation of burst size. To specifically measure the impact of long-range chromatin contacts on transcriptional bursting, we forced an LCR-β-globin promoter chromatin loop. We observed that raising contact frequencies increases burst fraction but not burst size. In cells in which two developmentally distinct LCR-regulated globin genes are cotranscribed in cis, burst sizes of both genes are comparable. However, allelic co-transcription of both genes is statistically disfavored, suggesting mutually exclusive LCR-gene contacts. These results are consistent with competition between the β-type globin genes for LCR contacts and suggest that LCR-promoter loops are formed and released with rapid kinetics.

PMID:
27067601
PMCID:
PMC4842148
DOI:
10.1016/j.molcel.2016.03.007
[Indexed for MEDLINE]
Free PMC Article

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