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47 Analysis of SPT Genes: A Genetic Approach toward Analysis of TFIID, Histones, and Other Transcription Factors of Yeast

Fred Winston


Insertion mutations in Saccharomyces cerevisiae, caused by Ty elements or Ty long terminal repeats (δ sequences), can disrupt expression of adjacent genes by inhibiting or otherwise altering normal transcription. Selection for suppressors of these insertion mutations has resulted in the isolation of mutations that identify a large set of genes (SPT genes) required for normal transcription. Genetic and molecular analysis has placed most SPT genes into two groups. The first group includes SPT15, which encodes the TATA-binding factor TFIID. The second group includes SPT11 and SPT12, which encode histones H2A and H2B, respectively. Each group also contains other genes that encode previously unidentified functions that are related to the functions of TFIID and histones. Most SPT genes identified are essential or important for growth, indicating that these genes are critical for normal transcription in vivo.

In the yeast S. cerevisiae many genes involved in the regulation of gene expression have been identified by mutant isolation and analysis. In most such cases, mutants have been isolated by a particular genetic selection or screen for altered expression of a gene or of a set of genes. Subsequent analyses of the genes thus identified have led to fundamental insights into the nature of gene expression in yeast. Some prominent examples of this approach are studies on general amino acid control (Hinnebusch 1988), mating type regulation (Herskowitz and Oshima 1981; Nasmyth and Shore 1987), regulation of GAL genes (Johnston 1987), and regulation of CYC 1 (Guarente 1987).

Many of the observations derived...

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