Identification of Mutant Versions of the Spt16 Histone Chaperone That Are Defective for Transcription-Coupled Nucleosome Occupancy in Saccharomyces cerevisiae

摘要

The highly conserved FACT (Facilitates Chromatin Transactions) complex performs essential functions in eukaryotic cells through the reorganization of nucleosomes. During transcription, FACT reorganizes nucleosomes to allow passage of RNA Polymerase II and then assists in restoring these nucleosomes after RNA Polymerase II has passed. We have previously shown, consistent with this function, that facilitates repression of the Saccharomyces cerevisiae gene by maintaining nucleosome occupancy over the promoter of this gene as a consequence of intergenic transcription of noncoding DNA. In this study, we report the results of a genetic screen to identify mutations in that derepress . Twenty-five mutant alleles were found to derepress without causing significant reductions in either RNA levels or protein levels. Additional phenotypic assays indicate that these mutants have general transcription defects related to altered chromatin structure. Our analyses of a subset of these mutants reveal defects in transcription-coupled nucleosome occupancy over the promoter. We provide evidence that these mutants broadly impair transcription-coupled nucleosome occupancy at highly transcribed genes but not at lowly transcribed genes. Finally, we show that one consequence shared by these mutations is the reduced binding of mutant proteins across and other highly transcribed genes. Taken together, our results highlight an important role for in orchestrating transcription-coupled nucleosome assembly at highly transcribed regions of the genome, possibly by facilitating the association of during this process.