Regulation of RNA polymerase II transcription by the SPT proteins in yeast Saccharomyces cerevisiae

Abstract

Transcription of protein-encoding genes by RNA polymerase II is a critical step in controlling cellular homeostasis, proliferation and differentiation, and requires concerted functions of a large number of transcription factors to precisely decipher the information packaged in the genome. While some factors regulate transcription by promoting the recruitment of TFIID/TBP or the assembly of the preinitiation complex, others functions at the post-recruitment steps. A group of transcription factors that are highly conserved throughout evolution, collectively known as Spt proteins, are particularly important for transcription regulation because their involvement in both recruitment functions and the post-recruitment functions. The yeast SPN1 is an essential and highly conserved SPT gene that has been implicated in regulating RNA polymerase II transcription by post-recruitment functions. To understand how Spn1 regulates RNA polymerase II transcription, a genetic screen was developed to target the functions of Spn1. The results of the genetic screen revealed the involvement of Spn1 in maintaining the chromatin structure and regulating the elongation. Further analysis defined a critical role of Spn1 in coordinating recruitment of the chromatin-remodeling complex, Swi/Snf and the nucleosome reassembly factor, Spt6. To get a better understanding of the functions of other Spt proteins during transcription, we analyzed the behavior of some non-essential Spt proteins and certain SAGA subunits in the artificial recruitment assays, and their effects on the transcription of genes that are regulated by the post-recruitment functions. Our initial results showed that while some Spt proteins function to regulate the recruitment of TBP/TFIID to the promoters, others affect the transcription after TBP recruitment. Furthermore, we showed that additional functions of the SAGA complex are required for post-recruitment regulation besides its roles in histone acetylation and TBP recruitment. These studies provide valuable information to understand the mechanistic functions of various Spt proteins in regulating RNA polymerase II transcription.