The macrolide antibiotic rapamycin inhibits cellular proliferation by interfering with the highly conserved TOR (for target of rapamycin) signaling pathway. Growth arrest of budding yeast cells treated with rapamycin is followed by the program of molecular events that characterizes entry into G 0 (stationary phase), including the induction of polymerase (Pol) II genes typically expressed only in G 0 . Normally, progression into G 0 is characterized by transcriptional repression of the Pol I and III genes. Here, we show that rapamycin treatment also causes the transcriptional repression of Pol I and III genes. The down-regulation of Pol III transcription is TOR dependent. While it coincides with translational repression by rapamycin, transcriptional repression is due in part to a translation-independent effect that is evident in extracts from a conditional tor2 mutant. Biochemical experiments reveal that RNA Pol III and probably transcription initiation factor TFIIIB are targets of repression by rapamycin. In view of previous evidence that TFIIIB and Pol III are inhibited when protein phosphatase 2A (PP2A) function is impaired, and that PP2A is a component of the TOR pathway, our results suggest that TOR signaling regulates Pol I and Pol III transcription in response to nutrient growth signals.Gradual nutrient depletion in Saccharomyces cerevisiae provokes a broad spectrum of morphological and biochemical changes that result in a terminal cell cycle arrest phenotype called G 0 or stationary phase (reviewed in references 44 and 45). Stationary-phase cells have a 1n DNA content, are uniformly large and unbudded, and display a prominent vacuole. The G 0 state is further characterized by reduced protein synthesis, and the pattern of RNA polymerase (Pol) II transcripts is distinct in cycling and G 0 cells. Thus, more than 95% of Pol II genes are repressed in G 0 , and a subset of Pol II genes whose products promote survival under conditions of nutrient limitation are massively induced at the transcriptional level (8). Induction of the G 0 pattern of Pol II transcription in yeast accompanies the repression of transcription of the large rRNA genes by Pol I and the tRNA and 5S rRNA genes by Pol III (9,26,33,36). Since tRNA and rRNA synthesis accounts for about 70% of nuclear transcription, this regulatory mechanism may enhance survival in G 0 by limiting the energetically costly production of relatively stable RNA products not immediately required for viability.While there is striking repression of translation in G 0 , some critical aspects of the stationary-phase response are not simply downstream consequences of a decreased rate of protein synthesis. For example, treatment of cultures with cycloheximide does not cause the accumulation of large unbudded cells or cells with a 1n DNA content (6), and in some strains there is no inhibition of Pol I or Pol III transcription in extracts from cells treated with cycloheximide (9). Key physiological steps in the differentiation of a stationary-phase cell are therefore likely to...

We purified xUBF on the basis of its ability to specifically bind the enhancer elements of the Xenopus laevis rRNA genes. xUBF also binds to both upstream and downstream regions of the X. laevis ribosomal gene promoter and is essential for polymerase I transcription. Unexpectedly, xUBF binds to both upstream and downstream regions of the human ribosomal gene promoter, producing footprints that are indistinguishable from the footprints produced by hUBF, a previously described polymerase I transcription factor isolated from human cells. Despite extensive sequence divergence of vertebrate polymerase I promoters, these data suggest an evolutionary conservation of the primary DNA-protein interaction.

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Here we report that RNA polymerase (pol) III transcription is repressed in response to DNA damage by downregulation of TFIIIB, the core component of the pol III transcriptional machinery. Protein kinase CK2 transduces this stress signal to TFIIIB. CK2 associates with and normally activates the TATA binding protein (TBP) subunit of TFIIIB. The beta regulatory subunit of CK2 binds to TBP and is required for high TBP-associated CK2 activity and pol III transcription in unstressed cells. Transcriptional repression induced by DNA damage requires CK2 and coincides with downregulation of TBP-associated CK2 and dissociation of catalytic subunits from TBP-CK2 complexes. Therefore, CK2 is the terminal effector in a signaling pathway that represses pol III transcription when genome integrity is compromised.

Little is known about what enzyme complexes or mechanisms control global lysine acetylation in the amino-terminal tails of the histones. Here, we show that glucose induces overall acetylation of H3 K9, 18, 27 and H4 K5, 8, 12 in quiescent yeast cells mainly by stimulating two KATs, Gcn5 and Esa1. Genetic and pharmacological perturbation of carbon metabolism, combined with 1H-NMR metabolic profiling, revealed that glucose induction of KAT activity directly depends on increased glucose catabolism. Glucose-inducible Esa1 and Gcn5 activities predominantly reside in the picNuA4 and SAGA complexes, respectively, and act on chromatin by an untargeted mechanism. We conclude that direct metabolic regulation of globally acting KATs can be a potent driving force for reconfiguration of overall histone acetylation in response to a physiological cue.