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Mutations that suppress the deletion of an upstream activating sequence in yeast: Involvement of a protein kinase and histone H3 in repressing transcription in vivo

Department of Genetics, Harvard Medical School, Boston, Massachusetts 02115.
Genetics (Impact Factor: 4.87). 12/1993; 135(3):665-76.
Source: PubMed

ABSTRACT Regulated transcription of most protein-encoding genes in Saccharomyces cerevisiae requires an upstream activating sequence (UAS); in the absence of UAS elements, little or no transcription occurs. In certain mutant strains, however, promoters that have been deleted for their UAS can direct significant levels of transcription, indicating that the remaining promoter elements (the basal promoter) are capable of directing higher levels of transcription, but they are normally represented in wild-type strains. To analyze this repression, we have selected for mutations that cause increased transcription of the SUC2 gene in the absence of its UAS. In addition to some previously studied genes, this selection has identified five genes that we have designated BUR1, BUR2, BUR3, BUR5 and BUR6 (for Bypass UAS Requirement). The bur mutations cause pleiotropic phenotypes, indicating that they affect transcription of many genes. Furthermore, some bur mutations suppress the requirement for the SNF5 trans-activator at both SUC2 and Ty. Additional analysis has demonstrated that BUR1 is identical to SGV1, which encodes a CDC28-related protein kinase. This result indicates that protein phosphorylation is important for repression of the SUC2 basal promoter as well as other aspects of transcription in vivo. Finally, BUR5 is identical to HHT1, encoding histone H3, further implicating chromatin structure as important for expression of SUC2.

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    • "The SPT genes encode many proteins important in transcription, including subunits of the SAGA histone-modifying complex (Grant et al. 1998), TBP itself, and histones (Clark-Adams et al. 1988; Winston and Sudarsanam 1998; Yamaguchi et al. 2001). SPT10 is not an essential gene, but the null allele is associated with very slow growth and defects in gene regulation (Denis and Malvar 1990; Natsoulis et al. 1991; Prelich and Winston 1993; Yamashita 1993; Dollard et al. 1994; Natsoulis et al. 1994). Spt10 contains a histone acetyltransferase (HAT) domain similar to that of Gcn5 (Neuwald and Landsman 1997), but it has not been possible to demonstrate HAT activity, despite many attempts by our laboratory and others. "
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    • "First, it was shown that suppressors of snf2/swi2 mutations included mutations in HTA1-HTB1, encoding histones H2A-H2B, and in SPT6, encoding a histone chaperone (Neigeborn et al. 1986, 1987; Clark-Adams and Winston 1987; Hirschhorn et al. 1992). This genetic relationship between Swi/Snf and chromatin was fortified by other results that showed that suppressors of swi1, swi2, and swi3 mutations were in histone H3-and H4-encoding genes (Prelich and Winston 1993; Kruger et al. 1995). Thus, genetics suggested that the transcriptional activation defects caused by loss of Swi/Snf could be bypassed by reducing or altering nucleosome function. "
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    • "Notably , we were aided in our identification of three of the complementation groups—EWE3/MED7, EWE4/SRB7, and EWE5/NUT2—by use of a novel conditional growth phenotype, enhanced sensitivity to 300 mm urea. It is surprising that our screen failed to pull out genes encoding chromatin-associated proteins, especially since a previous screen, using a similar strategy (selection of bypass suppressors of a UAS deletion, in the earlier case of SUC2), isolated recessive mutations in several chromatin-associated proteins, including H2A, H2B, H3, Spt6, Spt10, and Spt16, in addition to three others: Bur1 and Bur2, which compose a cyclin/cyclindependent kinase heterodimer, and Bur6, a subunit of the heterodimeric NC2 negative general transcription factor (Prelich and Winston 1993). The EWE screen isolated none of these. "
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