Browsing by Author "Stargell, Laurie, advisor"
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Item Open Access Mechanisms of RNA polymerase II-mediated transcription(Colorado State University. Libraries, 2007) Fletcher, Aaron Glenn Louis, author; Stargell, Laurie, advisorTranscription by RNA Polymerase II (RNAPII) is a critical step in controlling biological events such as cell growth, cell differentiation, response to environmental change, homeostasis, and disease. The regulation of transcription initiation of some genes is controlled at the level of TBP and RNAPII recruitment to the promoter. At such genes, the binding of TBP/RNAPII is the rate-limiting step for gene expression. Other genes already have TBP/RNAPII occupying the promoter before induction of gene expression, and the rate limiting step is no longer recruitment of TBP/RNAPII. These genes are collectively known as post-recruitment regulated genes. The yeast CYC1 gene is a post-recruitment regulated gene and serves as an excellent model for understanding the mechanism behind post-recruitment regulation. A TBP recruitment bypass screen was developed to investigate the mechanism of post-recruitment regulation. The results of the bypass screen revealed that SAGA and Mediator play important roles in post-recruitment regulation. Further analysis of SAGA uncovered a new function: that suggests SAGA is important in recruitment of Mediator to post-recruitment regulated genes. In addition to RNAPII and TBP, the CYC1 gene was found to have TFIIH, capping enzyme and serine 5 phosphorylation of the RNAPII C-terminal domain occupying the promoter in the uninduced condition. These results indicate that much of the Pre-Initiation Complex (PIC) occupies the CYC1 promoter in the uninduced state. In addition to PIC occupancy at CYC1, a conserved and essential protein, Spn1, is found to occupy the promoter during uninduced conditions. To further understand the role of this essential protein, genome localization studies and transcription profiling were performed. These studies suggest that in addition to playing an important role in post-recruitment regulation of gene expression, Spn1 may be involved in the transcription of ribosomal proteins. Taken together, this body of work contributes significantly to understanding the regulatory mechanisms of post-recruitment regulation.Item Open Access New functions of the SAGA complex in regulation of transcription by RNA polymerase II(Colorado State University. Libraries, 2008) Chen, Xu, author; Stargell, Laurie, advisorThe yeast SAGA (Spt-Ada-Gcn5-acetyltransferase) complex plays a role in Gal4-mediated transcriptional activation via delivery of TATA-binding protein (TBP) to Gal4-responsive promoters. Little is known about the impact of the sequence of the TATA element in the core promoter in this process. To investigate the SAGA complex regulatory function at different TATA element sequences, we compared a consensus element (TATA) to an off-consensus element (CATA) in the kinetics of Gal4-dependent gene activation, PIC occupancy, the requirement of SAGA components, and the histone acetylation state. We have found a new function of SAGA carried by subunits Gcn5, Ada2 and Spt8: TATA-element-censoring. This function enhances transcription driven by the consensus TATA element and represses transcription driven by off-consensus TATA elements. This functions works at both synthetic promoters and the endogenous GAL promoters. Via a genetic screen, Swi/Snf and RSC complexes were also identified with TATA-censoring function. Our study suggests that the new function involves TBP delivery, histone acetylation and histone eviction.Item Open Access Spn1, a multifunctional player in the chromatin context(Colorado State University. Libraries, 2016) Li, Sha, author; Stargell, Laurie, advisor; Argueso, J. Lucas, committee member; Hansen, Jeffrey, committee member; Luger, Karolin, committee member; Yao, Tingting, committee memberSpn1 was initially identified as a transcription factor that copurified with Spt6. Spn1 functions in transcription initiation and elongation, mRNA processing and export, histone modification, as well as in heterochromatic silencing. Our recent study demonstrated that Spn1 could bind histones and assemble nucleosomes in vitro. Therefore, Spn1 is a new member of the histone chaperone family. Here we found that Spt6 regulates Spn1-nucleosome interaction and conversely, Spn1 regulates Spt6-H2A-H2B interaction. Co-regulation between Spn1 and Spt6 enables them to be independent histone chaperones in nucleosome assembly. In addition, abrogation of Spn1-Spt6 interaction does not generate cryptic transcripts at certain genes. Furthermore, we identified a new interaction between Spn1 and the histone chaperone Nap1. Spn1, Nap1 and histones can form a large complex. We also found Spt6 could compete Nap1 for Spn1 binding, therefore disrupting Spn1-Nap1 interaction and releasing Nap1. In sum, Spn1 plays a multifunctional role in the chromatin context via dynamic interactions with its binding partners.Item Open Access The chromatin binding factor Spn1 contributes to genome instability in Saccharomyces cerevisiae(Colorado State University. Libraries, 2018) Thurston, Alison K., author; Stargell, Laurie, advisor; Bailey, Susan, committee member; DeLuca, Jennifer, committee member; Hansen, Jeffrey, committee member; Luger, Karolin, committee memberMaintaining the genetic information is the most important role of a cell. Alteration to the DNA sequence is generally thought of as harmful, as it is linked with many forms of cancer and hereditary diseases. Contrarily, some level of genome instability (mutations, deletions, amplifications) is beneficial to an organism by allowing for adaptation to stress and survival. Thus, the maintenance of a "healthy level" of genome stability/instability is a highly regulated process. In addition to directly processing the DNA, the cell can regulate genome stability through chromatin architecture. The accessibility of DNA for cellular machinery, damaging agents and spontaneous recombination events is limited by level of chromatin compaction. Remodeling of the chromatin for transcription, repair and replication occurs through the actions of ATP remodelers, histone chaperones, and histone modifiers. These complexes work together to create access for DNA processing and to restore the chromatin to its pre-processed state. As such, many of the chromatin architecture factors have been implicated in genome stability. In this study, we have examined the role of the yeast protein Spn1 in maintaining the genome. Spn1 is an essential and conserved transcription elongation factor and chromatin binding factor. As anticipated, we observed that Spn1 contributes to the maintenance of the genome. Unexpectedly, our data revealed that Spn1 contributes to promoting genome instability. Investigation into a unique growth phenotype in which cells expressing a mutant form of Spn1 displayed resistance to the damaging agent, methyl methanesulfonate revealed Spn1 influences pathway selection during DNA damage tolerance. DNA damage tolerance is utilized during replication and G2 to bypass lesions, which could permanently stall replication machinery. This pathway congruently promotes and prevents genome instability. We theorize that these outcomes are due to the ability of Spn1 to influence chromatin structure throughout the cell cycle.