PgmNr Y3109: Role of chromatin modulators during polymerase switch for ribosomal RNA synthesis in Saccharomyces cerevisiae.

Authors:
KUSHAL BHATT; Heather Conrad-Webb


Institutes
TEXAS WOMAN'S UNIVERSITY, DENTON, TX.


Keyword: Transcription

Abstract:

Ribosomal RNA synthesis consumes major portion of the cellular resources necessitating its strict regulation. Under non-stress conditions RNA polymerase I (Pol I) synthesizes a 35S precursor rRNA, but during stress (nitrogen deprivation) synthesis also occurs by RNA polymerase II (Pol II) from a cryptic site upstream of Pol I binding site. This polymerase switch has been observed in higher eukaryotes leading to the hypothesis that the switch serves as back up mechanism for rRNA synthesis during stress allowing the survival of the cell. Pol II rRNA synthesis may be followed using an rDNA-LacZ reporter construct. Nitrogen deprivation leads to a three-fold increase in the b-galactosidase activity. The corepressor Ssn6-Tup1 is known to repress transcription, when recruited to target promoters by repressor proteins. Absence of this corepressor leads to an increase in enzyme activity under normal and stress conditions. Furthermore, the absence of repressor proteins Sko1, Nrg1, Sut1 that are known to recruit Ssn6-Tup1 also showed an increase in b-galactosidase activity. Hmo1, a High Mobility Group protein, binds to rDNA to regulate pol I rRNA synthesis. As expected b-galactosidase activity increases significantly in the absence of Hmo1 in both non-stress and stress conditions . We hypothesize that stress signaling pathways will signal these repressors to inhibit their silencing function. Repressor complexes will be investigated during normal growth and stress for secondary modifications and their binding to rDNA. These studies will help dissect the regulation of rRNA synthesis and cell survival mechanisms under stress conditions.



Yeast Database Genetic Index
1. gene symbol: HMO1; systematic name: YDR174W
2. gene symbol: SSN6; systematic name: YBR112C
3. gene symbol: TUP1; systematic name: YCR084C
4. gene symbol: NRG1; systematic name: YDR043C
5. gene symbol: SKO1; systematic name: YNL167C
6. gene symbol: SUT1; systematic name: YGL162W