Activator-Independent Functions of the Yeast Mediator Sin4 Complex in Preinitiation Complex Formation and Transcription Reinitiation
AUTOR(ES)
Reeves, Wendy M.
FONTE
American Society for Microbiology
RESUMO
RNA polymerase II (Pol II) Mediator plays an essential role in both basal and activated transcription. Previously, subunits of the Sin4 Mediator complex (Sin4, Pgd1, Gal11, and Med2) have been implicated in both positive and negative transcriptional regulation. Furthermore, it was proposed that this subcomplex constitutes an activator-binding domain. A yeast nuclear-extract system was used to investigate the biochemical role of the Sin4 complex. In contrast to previous findings, we found at least two general activator-independent roles for the Sin4 complex. First, mutations in sin4 and pgd1 destabilized the Pol II-Med complex, leading to a reduced rate and extent of preinitiation complex (PIC) formation both in the presence and absence of activators. Although reduced in amount compared with the wild type, PICs that are formed lacking the Sin4 complex are stable and can initiate transcription normally. Second, mutation of pgd1 causes partial disruption of the Sin4 complex and leads to a defect in transcription reinitiation. This defect is caused by dissociation of mutant Mediator from promoters after initiation, leading to nonfunctional Scaffold complexes. These results show that function of the Sin4 complex is not essential for transcription activation in a crude in vitro system but that it plays key roles in the general transcription mechanism.
ACESSO AO ARTIGO
http://www.pubmedcentral.nih.gov/articlerender.fcgi?artid=140685Documentos Relacionados
- Requirement of TRAP/Mediator for Both Activator-Independent and Activator-Dependent Transcription in Conjunction with TFIID-Associated TAFIIs
- Activator-Independent Gene Expression in Neurospora Crassa
- Activator-dependent and activator-independent defective recombinant retroviruses from bovine leukemia virus.
- Yeast global transcriptional regulators Sin4 and Rgr1 are components of mediator complex/RNA polymerase II holoenzyme.
- The Yeast Hrs1 Gene Is Involved in Positive and Negative Regulation of Transcription and Shows Genetic Characteristics Similar to Sin4 and Gal11