Dynamics of protein folding and subunit interactions in assembly of the yeast mediator complex

The Mediator complex was originally discovered in the yeast Saccharomyces cerevisiae and has since then been shown to be required for transcriptional regulation both in vitro and in vivo. The Mediator complex also stimulates basal, unregulated transcription and serves as a bridge by conveying signal...

Full description

Bibliographic Details
Main Author: Shaikhibrahim, Zaki
Format: Doctoral Thesis
Language:English
Published: Umeå universitet, Medicinsk kemi och biofysik 2009
Subjects:
Online Access:http://urn.kb.se/resolve?urn=urn:nbn:se:umu:diva-29976
http://nbn-resolving.de/urn:isbn:978-91-7264-854-8
id ndltd-UPSALLA1-oai-DiVA.org-umu-29976
record_format oai_dc
spelling ndltd-UPSALLA1-oai-DiVA.org-umu-299762013-01-08T13:05:44ZDynamics of protein folding and subunit interactions in assembly of the yeast mediator complexengShaikhibrahim, ZakiUmeå universitet, Medicinsk kemi och biofysikUmeå : Umeå university2009mediatortranscriptional regulationassemblyfoldingMEDICINEMEDICINThe Mediator complex was originally discovered in the yeast Saccharomyces cerevisiae and has since then been shown to be required for transcriptional regulation both in vitro and in vivo. The Mediator complex also stimulates basal, unregulated transcription and serves as a bridge by conveying signals from promoter-bound transcriptional regulatory proteins such as activators and repressors to the RNA Polymerase II general transcriptional machinery. The Mediator consists of 21 subunits and can be divided into three distinct modules head, middle and tail. Despite the tremendous progress that has been achieved so far in characterizing the Mediator complex both functionally and structurally, many aspects of the complex are not yet well understood. The objective of this work is to achieve further understanding of the Mediator complex by studying the folding of different protein subunits, their interactions and how that affects assembly of the Mediator complex. In our first study we made a temperature-sensitive med21 mutant and used it to identify genes that can suppress the mutation when present in high copy number. Among the 10 genes that we identified, the strongest suppressors were Med7 and Med10, which encode Mediator subunits, and Ash1, which encodes a repressor of the HO gene. We also used 2-hybrid experiments and immunoprecipitation to study protein-protein interactions between Med21 and the Med4, Med7 and Med10 proteins which are all essential for viability and located within the middle domain of the Mediator complex. We found that the N-terminal 2-8 amino acids of Med21 are required for interactions with Med7 and Med10. These results led us to propose a model in which the N-terminal part of Med21 functions as a molecular switchboard where competing signals from various activators, repressors and mediator subunits are integrated prior to reaching the general transcription machinery. In our second study, we extended our studies of protein-protein interactions to another part of the mediator complex by studying the folding and the assembly processes of the mediator head domain subunits Med8, Med18 and Med20. Using purified proteins and a combination of several different methods such as immunoprecipitation, far-UV circular dichroism and fluorescence, we demonstrated that the Med8, Med18 and Med20 subunits are interdependent on each other for proper folding and complex formation. Doctoral thesis, comprehensive summaryinfo:eu-repo/semantics/doctoralThesistexthttp://urn.kb.se/resolve?urn=urn:nbn:se:umu:diva-29976urn:isbn:978-91-7264-854-8Umeå University medical dissertations, 0346-6612 ; 1290application/pdfinfo:eu-repo/semantics/openAccess
collection NDLTD
language English
format Doctoral Thesis
sources NDLTD
topic mediator
transcriptional regulation
assembly
folding
MEDICINE
MEDICIN
spellingShingle mediator
transcriptional regulation
assembly
folding
MEDICINE
MEDICIN
Shaikhibrahim, Zaki
Dynamics of protein folding and subunit interactions in assembly of the yeast mediator complex
description The Mediator complex was originally discovered in the yeast Saccharomyces cerevisiae and has since then been shown to be required for transcriptional regulation both in vitro and in vivo. The Mediator complex also stimulates basal, unregulated transcription and serves as a bridge by conveying signals from promoter-bound transcriptional regulatory proteins such as activators and repressors to the RNA Polymerase II general transcriptional machinery. The Mediator consists of 21 subunits and can be divided into three distinct modules head, middle and tail. Despite the tremendous progress that has been achieved so far in characterizing the Mediator complex both functionally and structurally, many aspects of the complex are not yet well understood. The objective of this work is to achieve further understanding of the Mediator complex by studying the folding of different protein subunits, their interactions and how that affects assembly of the Mediator complex. In our first study we made a temperature-sensitive med21 mutant and used it to identify genes that can suppress the mutation when present in high copy number. Among the 10 genes that we identified, the strongest suppressors were Med7 and Med10, which encode Mediator subunits, and Ash1, which encodes a repressor of the HO gene. We also used 2-hybrid experiments and immunoprecipitation to study protein-protein interactions between Med21 and the Med4, Med7 and Med10 proteins which are all essential for viability and located within the middle domain of the Mediator complex. We found that the N-terminal 2-8 amino acids of Med21 are required for interactions with Med7 and Med10. These results led us to propose a model in which the N-terminal part of Med21 functions as a molecular switchboard where competing signals from various activators, repressors and mediator subunits are integrated prior to reaching the general transcription machinery. In our second study, we extended our studies of protein-protein interactions to another part of the mediator complex by studying the folding and the assembly processes of the mediator head domain subunits Med8, Med18 and Med20. Using purified proteins and a combination of several different methods such as immunoprecipitation, far-UV circular dichroism and fluorescence, we demonstrated that the Med8, Med18 and Med20 subunits are interdependent on each other for proper folding and complex formation.
author Shaikhibrahim, Zaki
author_facet Shaikhibrahim, Zaki
author_sort Shaikhibrahim, Zaki
title Dynamics of protein folding and subunit interactions in assembly of the yeast mediator complex
title_short Dynamics of protein folding and subunit interactions in assembly of the yeast mediator complex
title_full Dynamics of protein folding and subunit interactions in assembly of the yeast mediator complex
title_fullStr Dynamics of protein folding and subunit interactions in assembly of the yeast mediator complex
title_full_unstemmed Dynamics of protein folding and subunit interactions in assembly of the yeast mediator complex
title_sort dynamics of protein folding and subunit interactions in assembly of the yeast mediator complex
publisher Umeå universitet, Medicinsk kemi och biofysik
publishDate 2009
url http://urn.kb.se/resolve?urn=urn:nbn:se:umu:diva-29976
http://nbn-resolving.de/urn:isbn:978-91-7264-854-8
work_keys_str_mv AT shaikhibrahimzaki dynamicsofproteinfoldingandsubunitinteractionsinassemblyoftheyeastmediatorcomplex
_version_ 1716508688096690176