Date of Award




Document Type


Degree Name

Doctor of Philosophy (PhD)


Department of Biomedical Sciences

Content Description

1 online resource (ii, xv, 188 pages) : illustrations (some color)

Dissertation/Thesis Chair

M. Joan Curcio

Committee Members

Todd Gray, Joseph Wade, JoEllen Welsh


Mediator Complex, Retrotransposition, RNA, Transcription, Ty1, Mobile genetic elements, Transposons, Saccharomyces cerevisiae, Genetic transcription

Subject Categories

Genetics | Molecular Biology


Retrotransposons are mobile genetic elements that replicate via an RNA intermediary and constitute a significant portion of most eukaryotic genomes. Saccharomyces cerevisiae has been invaluable to retrotransposon research due to the presence of an active retroelement known as Ty1. The mobility of Ty1 is regulated both positively and negatively by numerous host factors, including several subunits of the Mediator transcriptional co-activator complex. The Mediator core complex is organized into genetically and structurally defined head, middle, and tail modules, along with a transiently associated kinase module. We show that with the exception of the kinase module, deletion of non-essential subunits from Mediator modules has a major impact on Ty1 mobility. Disruption of the Mediator tail module decreases Ty1 retrotransposition to undetectable levels, while disruption of the head or middle module increases Ty1 mobility substantially. Mobility changes in these Mediator mutants do not correspond with significant differences in overall Ty1 RNA or Gag protein levels. The decreased mobility in tail module gene deletion mutants is dependent on the Ty1 promoter in the 5' LTR and is caused by increased expression of an internal transcript known as Ty1i, which encodes a dominant negative inhibitor of Ty1 retromobility. I present evidence that Mediator preferentially associates with the Ty1 or Ty1i core promoter in strains lacking specific Mediator head or tail subunits, respectively, indicating that Mediator controls Ty1 mobility by governing transcription start site selection at Ty1 elements via a mechanism of promoter competition.