Regulation of transcription elongation by P-TEFb is critical for proper gene expression and cell survival. The cell possesses large quantities of P-TEFb, but the vast majority of it is locked away and inactive in the 7SK snRNP. Since the discovery of the 7SK snRNP, research has been conducted to determine how P-TEFb is released from this complex. The goal of the research presented in this thesis is to better understand how the 7SK snRNP regulates P-TEFb and ultimately, gene expression.
This work documents the discovery and characterization of the 7SK stability protein LARP7. LARP7 is is associated with 7SK regardless of the presence of P-TEFb and HEXIM1. Stabilization of 7SK is essential for maintenance of the RNP because loss of LARP7 results in an increase in free P-TEFb and a significant reduction in the amount of 7SK. These results indicate that stabilization of the 7SK snRNP by LARP7 is important for regulating P-TEFb homeostasis.
Although P-TEFb was first characterized from Drosophila lysates, the conservation of the 7SK snRNP and the mechanisms regulating P-TEFb inhibition have not been described. Here, the Drosophila melanogaster homologues of LARP7 and 7SK are characterized. These studies show that the system of P-TEFb regulation is similar in flies and this makes Drosophila an attractive model system for studying P-TEFb regulation through embryonic and larval development.
Finally, factors and modifications involved in releasing P-TEFb directly are explored. An assay was developed for discovering proteins that can bind to and release P-TEFb from the 7SK snRNP. Use of this assay showed that post-translational modification of the components of the 7SK snRNP do not cause P-TEFb release directly. However, HIV Tat and the C-terminal P-TEFb binding region of the bromodomain containing protein, Brd4, are capable of extracting P-TEFb directly. Most importantly, the release of P-TEFb is followed by a conformational change in 7SK RNA that prevents the continued binding of HEXIM1 to the complex. P-TEFb release from the 7SK snRNP is the result of direct extraction of P-TEFb by viral or cellular proteins, and not post-translational modifications or a competition between HEXIM1 and hnRNP proteins for 7SK binding.
| Identifer | oai:union.ndltd.org:uiowa.edu/oai:ir.uiowa.edu:etd-2024 |
| Date | 01 December 2009 |
| Creators | Krueger, Brian |
| Contributors | Price, David H. |
| Publisher | University of Iowa |
| Source Sets | University of Iowa |
| Language | English |
| Detected Language | English |
| Type | dissertation |
| Format | application/pdf |
| Source | Theses and Dissertations |
| Rights | Copyright 2009 Brian J. Krueger |
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