![]() An array of genetic selections has been developed to identify factors affecting RNA pol II transcription. These systems have been instrumental not only for identifying the GTFs and their functions, but also for defining other transcription factors that influence the rate of transcription initiation.Ī second advantage of yeast is the potential to exploit the power of classical and molecular genetic methods to investigate fundamental biological problems. ![]() A second in vitro transcription system was derived from yeast whole-cell extracts ( 541, 542). ![]() In 1987, Lue and Kornberg established an in vitro transcription system derived from yeast nuclei that would accurately initiate transcription from exogenous template DNA ( 295). cerevisiae has proven to be extraordinarily valuable in these studies. Thus, the process of transcription initiation by RNA pol II is highly conserved among eukaryotic organisms, allowing for the experimental advantages offered by different organisms to be exploited to identify and define these factors. Similar work defined analogous factors in rats, Drosophila, and yeast, suggesting that the GTFs are indeed “general” factors, required for expression of most, perhaps all, class II genes. This activity provided an assay for the fractionation and subsequent identification of the GTFs, defined as factors required for accurate, basal-level transcription initiation in vitro ( 311). Although I emphasize the yeast system, I have attempted to integrate information from both yeast and metazoan systems whenever appropriate.Ī breakthrough in understanding the mechanism of transcription initiation followed the discovery in the laboratory of Roeder that purified RNA pol II would selectively and accurately initiate transcription from template DNA when supplemented with a crude cell extract ( 529). However, this subject cannot be considered separately from the RNA pol II core transcriptional machinery from higher eukaryotic organisms, where results obtained with human, rat and Drosophila systems have often led the way. I focus on the transcriptional machinery from the yeast Saccharomyces cerevisiae, emphasizing the combined roles of yeast genetics and biochemistry in defining factors and their associated functions. ![]() I discuss promoter elements and then review recent advances pertaining to three classes for transcription factors: general transcription factors (GTFs), transcriptional coactivators, and general transcriptional repressors. This review presents an overview of the RNA polymerase II (RNA pol II) core transcriptional machinery. Emphasis is placed on the role that yeast genetics has played in identifying these factors and their associated functions. This review focuses on the global effectors of RNA polymerase II transcription in yeast, including the general transcription factors, the coactivators, and the general repressors. General repressors either act through the core transcriptional machinery or are histone related and presumably affect chromatin function. Similar to coactivators, general transcriptional repressors affect the expression of a broad spectrum of genes yet do not repress all genes. Transcriptional repressors include both gene-specific and general factors. Accordingly, coactivators are neither gene-specific nor general transcription factors, although gene-specific coactivators have been described in metazoan systems. A third class of transcription factors, termed coactivators, is not required for basal transcription in vitro but often mediates activation by a broad spectrum of activators. Regulatory elements bind gene-specific factors, which affect the rate of transcription by interacting, either directly or indirectly, with components of the general transcriptional machinery. The core promoter is the site for assembly of the transcription preinitiation complex, which includes RNA pol II and the general transcription fctors TBP, TFIIB, TFIIE, TFIIF, and TFIIH. The eukaryotic promoter consists of core elements, which include the TATA box and other DNA sequences that define transcription start sites, and regulatory elements, which either enhance or repress transcription in a gene-specific manner. Transcription initiation by RNA polymerase II (RNA pol II) requires interaction between cis-acting promoter elements and trans-acting factors. ![]()
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