Molecular cloning of a gene encoding an ARS binding factor from the yeast Saccharomyces cerevisiae

The murine G+C-rich promoter binding protein mGPBP is required for promoter-specific transcription

The archetypal TATA-box deficient G+C-rich promoter of the murine adenosine deaminase gene (Ada) requires a 48-bp minimal self-sufficient promoter element (MSPE) for function. This MSPE was used to isolate a novel full-length cDNA clone that encodes a 66-kDa murine G+C-rich promoter binding protein (mGPBP). The mGPBP mRNAs are ubiquitously expressed as either 3.0- or 3.5-kb forms differing in 3' polyadenylation site usage. Purified recombinant mGPBP, in the absence of any other mammalian cofactors, binds specifically to both the murine Ada gene promoter's MSPE and the nonhomologous human Topo IIalpha gene's G+C-rich promoter. In situ binding assays, immunoprecipitation, and Western blot analyses demonstrated that mGPBP is a nuclear factor that can form complexes with TATA-binding protein, TFIIB, TFIIF, RNA polymerase II, and P300/CBP both in vitro and in intact cells. In cotransfection assays, increased mGPBP expression transactivated the murine Ada gene's promoter. Sequestering of GPBP present in HeLa cell nuclear extract by immunoabsorption completely and reversibly suppressed extract-dependent in vitro transcription from the murine Ada gene's G+C-rich promoter. However, transcription from the human Topo IIalpha gene's TATA box-containing G+C-rich promoter was only partially suppressed and the adenovirus major late gene's classical TATA box-dependent promoter is totally unaffected under identical assay conditions. These results implicate GPBP as a requisite G+C-rich promoter-specific transcription factor and provide a mechanistic basis for distinguishing transcription initiated at a TATA box-deficient G+C-rich promoter from that initiated at a TATA box-dependent promoter.

The sensing of nutritional status and the relationship to filamentous growth in Saccharomyces cerevisiae

Heterotrophic organisms rely on the ingestion of organic molecules or nutrients from the environment to sustain energy and biomass production. Non-motile, unicellular organisms have a limited ability to store nutrients or to take evasive action, and are therefore most directly dependent on the availability of nutrients in their immediate surrounding. Such organisms have evolved numerous developmental options in order to adapt to and to survive the permanently changing nutritional status of the environment. The phenotypical, physiological and molecular nature of nutrient-induced cellular adaptations has been most extensively studied in the yeast Saccharomyces cerevisiae. These studies have revealed a network of sensing mechanisms and of signalling pathways that generate and transmit the information on the nutritional status of the environment to the cellular machinery that implements specific developmental programmes. This review integrates our current knowledge on nutrient sensing and signalling in S. cerevisiae, and suggests how an integrated signalling network may lead to the establishment of a specific developmental programme, namely pseudohyphal differentiation and invasive growth.

A low-affinity estrogen-binding site in pregnant rat uteri: analysis and partial purification

We have identified a low-affinity (type II) estrogen-binding site (EBS) that is expressed at high levels during pregnancy in rat uteri. Although this activity was detectable in nonpregnant rat uteri, it was present in amounts (0.094 pmol/g of uteri) that were severalfold lower than the high-affinity type I estrogen receptor (0.57 pmol/g of uteri). During pregnancy, at 19-20 days of gestation, the low-affinity type II EBS became the major (> or = 88%) estrogen-binding site in rat uteri. The increase in the level of low-affinity EBS (7.9 pmol/g) in uteri was approximately 85-fold with an approximately 20-fold increase in the specific activity (0.39 pmol/mg) of this form, whereas the high-affinity form remained relatively unchanged. We report here a method of purification of type II EBS from pregnant rat uteri and present an analysis of its DNA and steroid-binding properties. Estradiol-binding studies and Scatchard analysis showed that the type II EBS had an apparent estradiol-binding affinity of > or = 24 nM. Gel filtration and SDS/PAGE analysis indicated that the type II EBS was a monomeric 73-kDa protein. The estradiol binding remained apparently uninhibited in the presence of a large excess of tamoxifen, nafoxidine, or dihydrotestosterone. Estradiol, diethylstilbestrol, and quercitin (a type II EBS-specific inhibitor) competed efficiently. The purified low-affinity EBS did not have sequence-specific DNA-binding activity with the estrogen-responsive element, which indicated that it differs in function from the type I estrogen receptor.

Role of multifunctional autonomously replicating sequence binding factor 1 in the initiation of DNA replication and transcriptional control in Saccharomyces cerevisiae

Autonomously replicating sequence (ARS) binding factor 1 (ABF1) is an abundant DNA-binding protein that specifically recognizes the motif RTCRYN5ACG at many sites in the yeast genome, including promoter elements, mating-type silencers, and ARSs. Mutational analysis of these sites suggests that ABF1 is involved in constitutive and carbon source-regulated transcriptional activation, transcriptional silencing, and ARS activity. To better assess the role of ABF1 in DNA replication and transcriptional control, temperature-sensitive lethal mutations in the ABF1 gene were isolated. Several of the abf1(Ts) strains show rapid growth arrest at the nonpermissive temperature. At the semipermissive temperature, these strains show an ARS-specific defect in the mitotic stability of ARS-CEN plasmids, such that the abf1 mutants show defects in ARS function identical to those of mutants bearing the mutations in the cis-acting ABF1 binding sites analyzed previously by numerous investigators. Flow cytometric analysis and in vivo DNA labeling experiments on an alpha-factor synchronized abf1(Ts) strain showed that at the nonpermissive temperature, these cells fail to progress efficiently from G1 through S phase and synthesize DNA at 25% of the level seen in the isogenic ABF1 strain. RNA synthesis is also reduced in the abf1(Ts) strains. In addition, transcriptional activation by an ABF1 binding site upstream activation sequence is completely defective in an abf1(Ts) strain at the semipermissive temperature. These phenotypes provide evidence that the same protein, ABF1, functions in the initiation of DNA replication and transcriptional activation.

Role of multifunctional autonomously replicating sequence binding factor 1 in the initiation of DNA replication and transcriptional control in Saccharomyces cerevisiae

Autonomously replicating sequence (ARS) binding factor 1 (ABF1) is an abundant DNA-binding protein that specifically recognizes the motif RTCRYN5ACG at many sites in the yeast genome, including promoter elements, mating-type silencers, and ARSs. Mutational analysis of these sites suggests that ABF1 is involved in constitutive and carbon source-regulated transcriptional activation, transcriptional silencing, and ARS activity. To better assess the role of ABF1 in DNA replication and transcriptional control, temperature-sensitive lethal mutations in the ABF1 gene were isolated. Several of the abf1(Ts) strains show rapid growth arrest at the nonpermissive temperature. At the semipermissive temperature, these strains show an ARS-specific defect in the mitotic stability of ARS-CEN plasmids, such that the abf1 mutants show defects in ARS function identical to those of mutants bearing the mutations in the cis-acting ABF1 binding sites analyzed previously by numerous investigators. Flow cytometric analysis and in vivo DNA labeling experiments on an alpha-factor synchronized abf1(Ts) strain showed that at the nonpermissive temperature, these cells fail to progress efficiently from G1 through S phase and synthesize DNA at 25% of the level seen in the isogenic ABF1 strain. RNA synthesis is also reduced in the abf1(Ts) strains. In addition, transcriptional activation by an ABF1 binding site upstream activation sequence is completely defective in an abf1(Ts) strain at the semipermissive temperature. These phenotypes provide evidence that the same protein, ABF1, functions in the initiation of DNA replication and transcriptional activation.