Abstract
Transcriptional elongation requires the concerted action of several factors that allow RNA polymerase II to advance through chromatin in a highly processive manner. In order to identify novel elongation factors, we performed systematic yeast genetic screening based on the GLAM (Gene Length-dependent Accumulation of mRNA) assay, which is used to detect defects in the expression of long transcription units. Apart from well-known transcription elongation factors, we identified mutants in the prefoldin complex subunits, which were among those that caused the most dramatic phenotype. We found that prefoldin, so far involved in the cytoplasmic co-translational assembly of protein complexes, is also present in the nucleus and that a subset of its subunits are recruited to chromatin in a transcription-dependent manner. Prefoldin influences RNA polymerase II the elongation rate in vivo and plays an especially important role in the transcription elongation of long genes and those whose promoter regions contain a canonical TATA box. Finally, we found a specific functional link between prefoldin and histone dynamics after nucleosome remodeling, which is consistent with the extensive network of genetic interactions between this factor and the machinery regulating chromatin function. This study establishes the involvement of prefoldin in transcription elongation, and supports a role for this complex in cotranscriptional histone eviction.
Highlights
IntroductionAfter the assembly of the preinitiation complex onto the promoter and the subsequent initiation of transcription, the enzymatic activity of RNA polymerase II enables the synthesis of considerably long RNA molecules in the elongation phase of transcription
RNA polymerase II transcribes nuclear protein-coding genes in eukaryotes
In this work we describe our finding of the transcriptional function of prefoldin by showing that it is present in the nucleus, binds chromatin in a transcription-dependent manner and contributes to chromatin dynamics during transcription elongation
Summary
After the assembly of the preinitiation complex onto the promoter and the subsequent initiation of transcription, the enzymatic activity of RNA polymerase II enables the synthesis of considerably long RNA molecules in the elongation phase of transcription During this process, nascent RNA is modified by capping and polyadenylation, exons are defined for splicing, while hnRNP components are recruited, ensuring the production of mature mRNAs that can be exported to the cytoplasm [1]. Nascent RNA is modified by capping and polyadenylation, exons are defined for splicing, while hnRNP components are recruited, ensuring the production of mature mRNAs that can be exported to the cytoplasm [1] This complexity explains the tight regulation of transcription elongation, which involves a large number of auxiliary factors. Factors like TFIIS stimulate the RNA cleavage activity of RNA polymerase II to enable it to resume transcription elongation [6,7,8]
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