Replication and Silencing at the Hmr-E Compound Origin in Saccharomyces Cerevisiae
Hurst, Simi Thomas
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https://hdl.handle.net/2142/86640
Description
Title
Replication and Silencing at the Hmr-E Compound Origin in Saccharomyces Cerevisiae
Author(s)
Hurst, Simi Thomas
Issue Date
2002
Doctoral Committee Chair(s)
David H. Rivier
Department of Study
Microbiology
Discipline
Microbiology
Degree Granting Institution
University of Illinois at Urbana-Champaign
Degree Name
Ph.D.
Degree Level
Dissertation
Keyword(s)
Biology, Molecular
Language
eng
Abstract
This study investigated the relationship between two distinct biological processes, replication and silencing, as they occur from the HMR locus. Within this locus, an 868 base pair (bp) region termed HMR-E functions as both a silencer and an origin of DNA replication. Replication activity assays of the HMR-E region revealed that it consisted of not one, but a minimum of three independent subregions capable of ARS (autonomously replicating sequence) and chromosomal origin activity. Each subregion was also tested for silencing ability, and one was subsequently classified as the 138bp minimal silencer-origin to reflect its unique capacity to act as both an independent origin and an independent silencer. The other two subregions (L and R) were designated non-silencer origins. Accordingly, HMR-E was termed a compound origin to reflect its novel organization. To determine the relationship between silencing and replication at HMR, mutational analysis of the sequence of the minimal silencer-origin was performed. Mutation of a sequence is required for silencing improved initiation efficiency. Mutation of a gene encoding a silencing protein resulted in decreased silencing and increased initiation efficiency. Conversely, mutation of a gene encoding a replication protein resulted in decreased initiation and improved silencing. This report also addressed the influence the non-silencer origins might have upon replication and silencing. This line of inquiry revealed that the non-silencer origins contributed to both replication and silencing at the HMR locus. HMR-I, which is located approximately 3.0kb telomere proximal to HMR-E, also contributed to both replication and silencing at HMR. The investigation presented here revealed several key features about the HMR locus. Firstly, the origin at HMR-E has been redefined to include the L and R subregions, as well as the 138bp silencer-origin. Secondly, the silencer is larger than previously defined and may be coincident with the compound origin. Thirdly, the mutation of silencer sequence elements and genes encoding proteins that promote one process, results in the improvement of the other process. Based upon our examination of the relationship between replication and silencing at HMR-E, we hypothesize that the processes of replication and silencing may compete with one another at the HMR locus.
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