Changes in histone gene dosage alter transcription in yeast.

Abstract

Chromatin structure is believed to be important for a number of cellular processes, including transcription. However, the role of nucleosomes in transcription is not well understood. We have identified the yeast histone locus HTB1-HTB1, encoding histones H2A and H2B, as a suppressor of solo 8 insertion mutations that inhibit adjacent gene expression. The HTA1-HTB1 locus causes suppression either when present on a high-copy-number plasmid or when mutant. These changes in HTA1-HTB1 alter transcription of the genes adjacent to the 8 insertions. On the basis of this result, we have examined the effects of increased and decreased histone gene dosage for all four yeast histone loci. From the types of histone gene dosage changes that cause suppression of insertion mutations, we conclude that altered stoichiometry of histone dimer sets can alter transcription in yeast. Many studies have demonstrated the presence of altered chromatin structure in transcriptionally active regions of the genome (for reviews, see Mathis et al. 1980;Pederson et al. 1986). However, other work has shown that the level of transcription does not affect chromatin structure at certain loci (Nasmyth 1982; for review, see Mathis et al. 1980). Thus, the cause-and-effect relationship between chromatin structure and transcription remains unclear.The major subunit of chromatin is the nucleosome, which consists of DNA wrapped around a histone octamer that is composed of two H2A-H2B dimers and an H3-H4 tetramer (for review, see Pederson et al. 1986). Since histones are the protein components of nucleosomes, it is reasonable to hypothesize that alteration of histone levels would affect chromatin structure. A genetic approach to study the effect of chromatin structure on transcription and other cellular processes would be to alter histone levels by mutation or by gene amplification and then to screen for resulting mutant phenotypes.Changes in histone levels have been reported to cause various phenotypes. Meeks-Wagner and Hartwell (1986) showed that a high copy number of the genes encoding H2A and H2B or of the genes encoding H3 and H4 causes increased chromosome loss during mitosis in Saccharomyces cerevisiae. Yeast cells depleted for H2B arrest in 3Present address: Program in Molecular Biology and Virology, Memorial

A New Class of Histone H2A Mutations in Saccharomyces cerevisiae Causes Specific Transcriptional Defects In Vivo

“…After transfer to media containing 5FOA, which selects for cells that have lost the URA3-marked plasmid carrying the wild-type HTA1-HTB1 locus, transformants were screened for recessive phenotypes. As an internal control for the level of mutagenesis, we also screened transformants for sensitivity to 5FOA, which indicates inability to lose the wild-type plasmid and therefore a complete loss-of-function mutation in HTA1, and suppression of the insertion mutation lys2-128␦, which probably indicates partial loss of function (18,31). Of 2,200 transformants tested, 83 were 5FOA resistant and 70 showed an Spt Ϫ phenotype, suggesting that the proportion of transformants carrying hta1 mutations was at least 6%.…”

“…No transcriptional role has previously been demonstrated for the N-terminal tails of histones H2A and H2B, although the presence of at least one of the two tails is required for viability (63). Also, a reduction of histone H2A-H2B gene dosage can restore transcription to certain inactivated promoters (18,30). These in vivo experiments, then, show that changes in histones can lead to many kinds of transcriptional defects.…”

A single copy of linker H1 genes is enough for proliferation of the DT40 chicken B cell line, and linker H1 variants participate in regulation of gene expression

“…Many in vivo studies have been performed on the new nature of core histones-in addition to the vital role in chromatin organization mentioned above, especially in yeasts (Hereford et al 1982;Meeks-Wagner & Hartwell 1986;Norris & Osley 1987;Osley & Lycan 1987;Clark-Adams et al 1988;Norris et al 1988;Grunstein 1990;Carr et al 1994;Hirschhorn et al 1995)because gene replacement experiments on them can be carried out easily. Moreover, it has been reported that in Saccharomyces cerevisiae, the deletion of H4 N-terminal residues 4-23 or mutagenesis of the acetylatable lysines in this region decreases the activation of the GAL1 promoter, while the deletion of N-terminal residues 4-15 of H3 or the mutagenesis of the acetylatable lysines causes a hyperactivation of GAL1 (Fisher-Adams & Grunstein 1995).…”

Regulation of Histone Gene Expression in Budding Yeast

“…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).…”