Two alternative pathways of transcription initiation in the yeast negative regulatory gene GAL80

Inference of large-scale gene regulatory networks using regression-based network approach

The gene regulatory network modeling plays a key role in search for relationships among genes. Many modeling approaches have been introduced to find the causal relationship between genes using time series microarray data. However, they have been suffering from high dimensionality, overfitting, and heavy computation time. Further, the selection of a best model among several possible competing models is not guaranteed that it is the best one. In this study, we propose a simple procedure for constructing large scale gene regulatory networks using a regression-based network approach. We determine the optimal out-degree of network structure by using the sum of squared coefficients which are obtained from all appropriate regression models. Through the simulated data, accuracy of estimation and robustness against noise are computed in order to compare with the vector autoregressive regression model. Our method shows high accuracy and robustness for inferring large-scale gene networks. Also it is applied to Caulobacter crescentus cell cycle data consisting of 1472 genes. It shows that many genes are regulated by two transcription factors, ctrA and gcrA, that are known for global regulators.

Prevalence of the initiator over the TATA box in human and yeast genes and identification of DNA motifs enriched in human TATA-less core promoters

The core promoter of eukaryotic genes is the minimal DNA region that recruits the basal transcription machinery to direct efficient and accurate transcription initiation. The fraction of human and yeast genes that contain specific core promoter elements such as the TATA box and the initiator (INR) remains unclear and core promoter motifs specific for TATA-less genes remain to be identified. Here, we present genome-scale computational analyses indicating that approximately 76% of human core promoters lack TATA-like elements, have a high GC content, and are enriched in Sp1-binding sites. We further identify two motifs - M3 (SCGGAAGY) and M22 (TGCGCANK) - that occur preferentially in human TATA-less core promoters. About 24% of human genes have a TATA-like element and their promoters are generally AT-rich; however, only approximately 10% of these TATA-containing promoters have the canonical TATA box (TATAWAWR). In contrast, approximately 46% of human core promoters contain the consensus INR (YYANWYY) and approximately 30% are INR-containing TATA-less genes. Significantly, approximately 46% of human promoters lack both TATA-like and consensus INR elements. Surprisingly, mammalian-type INR sequences are present - and tend to cluster - in the transcription start site (TSS) region of approximately 40% of yeast core promoters and the frequency of specific core promoter types appears to be conserved in yeast and human genomes. Gene Ontology analyses reveal that TATA-less genes in humans, as in yeast, are frequently involved in basic "housekeeping" processes, while TATA-containing genes are more often highly regulated, such as by biotic or stress stimuli. These results reveal unexpected similarities in the occurrence of specific core promoter types and in their associated biological processes in yeast and humans and point to novel vertebrate-specific DNA motifs that might play a selective role in TATA-independent transcription.

The RNA polymerase II core promoter

The events leading to transcription of eukaryotic protein-coding genes culminate in the positioning of RNA polymerase II at the correct initiation site. The core promoter, which can extend ~35 bp upstream and/or downstream of this site, plays a central role in regulating initiation. Specific DNA elements within the core promoter bind the factors that nucleate the assembly of a functional preinitiation complex and integrate stimulatory and repressive signals from factors bound at distal sites. Although core promoter structure was originally thought to be invariant, a remarkable degree of diversity has become apparent. This article reviews the structural and functional diversity of the RNA polymerase II core promoter.

A novel domain of the yeast heat shock factor that regulates its activation function

Heat shock factor Hsf1 of the yeast Saccharomyces cerevisiae binds to the heat shock element (HSE) of a subset of genes and activates their transcription in response to various environmental stresses. Hsf1 protein contains discrete domains respectively involved in DNA-binding, trimerization, transcription activation, and transcription repression. Here we have identified a novel domain rich in basic amino acids at the extreme C-terminus of Hsf1. Deletion or point mutations of the C-terminal basic region caused an inefficient heat shock response of genes containing noncanonical HSEs such as CUP1 and HSP26. The basic region is also essential for oxidative stress-inducible transcription of CUP1 by Hsf1. By contrast, it was dispensable for heat induction through the canonical HSE. We suggest that the basic region is a modulator involved in regulation of the Hsf1-mediated activation depending on the architecture of its binding site.

Intrinsically bent DNA in the promoter regions of the yeast GAAL1-10 and GAL80 genes

Circular permutation analysis has detected fairly strong sites of intrinsic DNA bending on the promoter regions of the yeast GAL1-10 and GAL80 genes. These bends lie in functionally suggestive locations. On the promoter of the GAL1-10 structural genes, strong bends bracket nucleosome B, which lies between the UAS(G) and the GAL1 TATA. These intrinsic bends could help position nucleosome B. Nucleosome B plus two other promoter nucleosomes protect the TATA and start site elements in the inactive state of expression but are completely disrupted (removed) when GAL1-10 expression is induced. The strongest intrinsic bend ( approximately 70 degrees ) lies at the downstream edge of nucleosome B; this places it approximately 30 base pairs upstream of the GAL1 TATA, a position that could allow it to be involved in GAL1 activation in several ways, including the recruitment of a yeast HMG protein that is required for the normally robust level of GAL1 expression in the induced state (Paull, T., Carey, M., and Johnson, R. (1996) Genes Dev. 10, 2769-2781). On the regulatory gene GAL80, the single bend lies in the non-nucleosomal hypersensitive region, between a GAL80-specific far upstream promoter element and the more gene-proximal promoter elements. GAL80 promoter region nucleosomes contain no intrinsically bent DNA.

Yeast chromatin structure and regulation of GAL gene expression

Yeast genomic DNA is covered by nucleosome cores spaced by short, discrete length linkers. The short linkers, reinforced by novel histone properties, create a number of unique and dynamic nucleosome structural features in vivo: permanent unpeeling of DNA from the ends of the core, an inability to bind even full 147 bp core DNA lengths, and facility to undergo a conformational transition that resembles the changes found in active chromatin. These features probably explain how yeast can maintain most of its genome in a transcribable state and avoid large-scale packaging away of inactive genes. The GAL genes provide a closely regulated system in which to study gene-specific chromatin structure. GAL structural genes are inactive without galactose but are highly transcribed in its presence; the expression patterns of the regulatory genes can account for many of the features of GAL structural gene control. In the inactive state, GAL genes demonstrate a characteristic promoter chromosomal organization; the major upstream activation sequence (UASG) elements lie in open, hypersensitive regions, whereas the TATA and transcription start sites are in nucleosomes. This organization helps implement gene regulation in this state and may benefit the organism. Induction of GAL expression triggers Gal4p-dependent upstream nucleosome disruption. Disruption is transient and can readily be reversed by a Gal80p-dependent nucleosome deposition process. Both are sensitive to the metabolic state of the cell. Induction triggers different kinds of nucleosome changes on the coding sequences, perhaps reflecting the differing roles of nucleosomes on coding versus promoter regions. GAL gene activation is a complex process involving multiple Gal4p activities, numerous positive and negative cofactors, and the histone tails. DNA bending and chromosomal architecture of the promoter regions may also play a role in GAL regulation. Regulator-mediated competition between nucleosomes and the TATA binding protein complex for the TATA region is probably a central aspect of GAL regulation and a focal point for the numerous factors and processes that contribute to it.

Transcription initiation mediated by initiator binding protein in Saccharomyces cerevisiae

Many instances of the initiator element in the core promoter of protein-coding genes have been reported in mammalian cells and their viruses, but only one has been reported in the yeast Saccharomyces cerevisiae at the GAL80 gene. The initiator element of GAL80 directs transcription by itself and interacts with a nuclear protein designated yeast initiator binding factor (yIF). Here we show that yIF in a partially purified sample binds the sequence from -18 to +10 of GAL80. By employing a selected and amplified binding procedure, we have determined the preferred sequence for yIF binding to be -2 CACTN +3 (N indicates any nucleotide). Binding affinity of selected sequences to yIF correlated with their initiator-directed transcription in vivo, suggesting that the yIF-initiator interaction mediates transcription from the initiator in yeast. We also suggest that sequences flanking the preferred sequence affect both yIF binding and initiator activity.

MGA2 or SPT23 is required for transcription of the delta9 fatty acid desaturase gene, OLE1, and nuclear membrane integrity in Saccharomyces cerevisiae

MGA2 and SPT23 are functionally and genetically redundant homologs in Saccharomyces cerevisiae. Both genes are implicated in the transcription of a subset of genes, including Ty retrotransposons and Ty-induced mutations. Neither gene is essential for growth, but mga2 spt23 double mutants are inviable. We have isolated a gene-specific activator, SWI5, and the Delta9 fatty acid desaturase of yeast, OLE1, as multicopy suppressors of an mga2Delta spt23 temperature-sensitive mutation (spt23-ts). The level of unsaturated fatty acids decreases 35-40% when the mga2Delta spt23-ts mutant is incubated at 37 degrees. Electron microscopy of these cells reveals a separation of inner and outer nuclear membranes that is sometimes accompanied by vesicle-like projections in the intermembrane space. The products of Ole1p catalysis, oleic acid and palmitoleic acid, suppress mga2Delta spt23-ts and mga2Delta spt23Delta lethality and restore normal nuclear membrane morphology. Furthermore, the level of the OLE1 transcript decreases more than 15-fold in the absence of wild-type Mga2p and Spt23p. Our results suggest that Mga2p/Spt23p control cell viability by stimulating OLE1 transcription.

Yeast Gal11 and transcription factor IIE function through a common pathway in transcriptional regulation

The global transcription regulator Gal11, a component of RNA polymerase II holoenzyme, is required for full expression of many genes in yeast. We previously reported that Gal11 binds the small (Tfa2) and large (Tfa1) subunits of the general transcription factor (TF) IIE through Gal11 functional domains A and B, respectively. Here we demonstrate that the C-terminal basic region in Tfa2 is responsible for binding to domain A, whereas both the N-terminal hydrophobic and internal glutamic acid-rich regions in Tfa1 are responsible for binding to domain B. Yeast cells bearing a C-terminal deletion encompassing the Gal11-interacting region in each of the two TFIIE subunits, being viable, exhibited no obvious phenotype. In contrast, combination of the two deletions (TFIIE-DeltaC) showed phenotypes similar to those of gal11 null mutations. The levels of mRNA from TATA-containing genes, but not from TATA-less genes, decreased in TFIIE-DeltaC to an extent comparable to that in the gal11 null mutant. Combination of TFIIE-DeltaC with a gal11 null mutation did not result in an enhanced effect, suggesting that both TFIIE and Gal11 act in a common regulatory pathway. In a reconstituted cell-free system, Gal11 protein stimulated basal transcription in the presence of wild-type TFIIE. Such a stimulation was not seen in the presence of TFIIE-DeltaC.

The type of basal promoter determines the regulated or constitutive mode of transcription in the common control region of the yeast gene pair GCY1/RIO1

The yeast genes, GCY1 and RIO1, are transcribed divergently from the 869-base pair intergenic region. GCY1 is inducible by galactose about 25-fold due to Gal4p-binding to a single UASGAL, whereas RIO1 is constitutively expressed. GCY1 has a TATA box obeying the consensus TATAAA, whereas the RIO1 5'-upstream region lacks such a motif. In vitro mutagenesis of the TATA motif of GCY1, on the one hand, and introduction of a TATA-element into the promoter of RIO1, on the other hand, as well as inversion of the intergenic region have revealed that transcription of GCY1 and RIO1 is only regulated by Gal4p when a consensus TATA motif is included in their core promoters but not in its absence. The data imply that only transcription complexes that assemble at a consensus TATA box are compatible with specific transactivators, such as Gal4p. As a result, the adjacent gene is subject to regulated expression. By contrast, if a consensus TATA sequence is absent, the initiation complex does not respond to regulatory transcription factors, and consequently, the respective gene is constitutively transcribed. On the other hand, we show that two blocks of homo-oligomeric (dA.dT) sequences do not function as boundary sequences that might confine regulatory action of Gal4p to GCY1.

Promoter structure-dependent functioning of the general transcription factor IIE in Saccharomyces cerevisiae

General transcription factor (TF) IIE is an essential component of the basal transcription complex for protein-encoding genes, which is widely conserved in eukaryotes. Here we analyzed requirement for TFIIE for transcription in vivo by using yeast Saccharomyces cerevisiae cells harboring mutations in the TFA1 gene encoding the larger one of the two subunits of TFIIE. Deletion analysis indicated that the N-terminal half of Tfa1 protein has an essential function to support the cell growth. In a temperature-sensitive tfa1 mutant cell, the steady-state level of bulk poly(A)+ RNA decreased rapidly at the restrictive temperature. Surprisingly, levels of several mRNAs, whose transcription is directed by the promoters lacking the typical TATA sequence, were not affected in the mutant cells at that temperature. This promoter-specific functioning of TFIIE was reproduced in a cell-free system composed of TFIIE-depleted nuclear extracts. These results strongly suggest that requirement for TFIIE varies in each gene depending on the promoter structures in vivo.

Core promoter elements are essential as selective determinants for function of the yeast transcription factor GAL11

The GAL11 gene product, which copurifies with RNA polymerase II holoenzyme, is necessary for full expression of many, but not all, genes in yeast. Here we shows that the GAL11 dependence of a gene for expression is determined by the core promoter structure. In the GAL80 gene, a gal11 null mutation caused reduction of TATA-dependent transcription, but exerted no effect on initiator-mediated transcription. GAL11 stimulated TATA-dependent transcription, but did not affect the TATA-independent transcription in HIS4. GAL11 was also required for transcription mediated by a canonical TATA sequence but not by a nonconsensus TATA sequence of HIS3. These results suggest that GAL11 is specifically involved in the transcription machinery formed on the TATA element.