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Mechanisms of RNA polymerase II-mediated transcription


Transcription 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.


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postrecruitment regulation
RNA polymerase II
molecular biology


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