George Thireos

Bio: George Thireos is an academic researcher from Foundation for Research & Technology – Hellas. The author has contributed to research in topics: Gene & Saccharomyces cerevisiae. The author has an hindex of 19, co-authored 30 publications receiving 2546 citations. Previous affiliations of George Thireos include Academy of Athens & University of Crete.

The complete DNA sequence of yeast chromosome III.

Abstract: The entire DNA sequence of chromosome III of the yeast Saccharomyces cerevisiae has been determined. This is the first complete sequence analysis of an entire chromosome from any organism. The 315-kilobase sequence reveals 182 open reading frames for proteins longer than 100 amino acids, of which 37 correspond to known genes and 29 more show some similarity to sequences in databases. Of 55 new open reading frames analysed by gene disruption, three are essential genes; of 42 non-essential genes that were tested, 14 show some discernible effect on phenotype and the remaining 28 have no overt function.

Two distinct yeast transcriptional activators require the function of the GCN5 protein to promote normal levels of transcription.

Abstract: When yeast cells are grown under conditions of amino acid limitation, transcription of amino acid biosynthetic genes is increased through the action of the GCN4 transcriptional regulator. gcn5 mutant strains exhibit poor growth under such conditions. We have established that GCN4 requires the function of GCN5 in order to promote normal levels of transcriptional activation. In addition, we have shown that GCN5 is also required for the activity of the HAP2--HAP3--HAP4 transcriptional activation complex, which mediates the transcription of genes involved in respiratory functions. Thus, GCN5 is a new member of the recently revealed general class of transcriptional regulators that collaborate with certain specific DNA binding activators to promote high levels of transcription. We have cloned and sequenced the GCN5 gene. The deduced GCN5 protein contains a region conserved in other yeast, Drosophila and human proteins, all members of this new class of transcriptional activators.

5' untranslated sequences are required for the translational control of a yeast regulatory gene

Abstract: In yeast, many genes encoding amino acid biosynthetic enzymes are subject to a common regulatory system called the general control of amino acid biosynthesis. The product of the regulatory gene GCN4 is required for an increase in transcription of general control-regulated genes when yeast are grown under amino acid-starvation conditions. In this report, we show that the expression of the GCN4 gene is regulated at the translational level: the efficiency of translation of the GCN4 mRNA is dramatically increased during growth under amino acid-starvation conditions. The complete nucleotide sequence of the GCN4 gene, presented here, reveals the existence of an unusually long 5' untranslated region in the corresponding mRNA. In vivo analysis of the effects of a deletion in this 5' leader has enabled us to define a region required for the translational regulation of the GCN4 mRNA.

The Gcn5 bromodomain co-ordinates nucleosome remodelling

Abstract: The access of transcription factors to eukaryotic promoters often requires modification of their chromatin structure, which is accomplished by the action of two general classes of multiprotein complexes1. One class contains histone acetyltransferases (HATs), such as Gcn5 in the SAGA complex2, which acetylate nucleosomal histones. The second class contains ATPases, such as Swi2 in the Swi/Snf complex3, which provide the energy for nucleosome remodelling. In several promoters these two complexes cooperate but their functional linkage is unknown4,5,6,7,8. A protein module that is present in all nuclear HATs, the bromodomain, could provide such a link9. The recently reported in vitro binding of a HAT bromodomain with acetylated lysines within H3 and H4 amino-terminal peptides10 indicates that this interaction may constitute a targeting step for events that follow histone acetylation. Here we use a suitable promoter to show that bromodomain residues essential for acetyl-lysine binding are not required in vivo for Gcn5-mediated histone acetylation but are fundamental for the subsequent Swi2-dependent nucleosome remodelling and consequent transcriptional activation. We show that the Gcn5 bromodomain stabilizes the Swi/Snf complex on this promoter.

Yap1p, a yeast transcriptional activator that mediates multidrug resistance, regulates the metabolic stress response.

Abstract: Overexpression of the YAP1 transcriptional activator renders yeast cells resistant to multiple metabolic inhibitors. In an effort to identify other gene products required for this phenotype we have isolated genomic mutations which neutralize this effect. One such mutation was further characterized and the affected gene was shown to be identical to TPS2 which encodes trehalose phosphate phosphatase, an enzyme catalysing the second step in trehalose biosynthesis. We have analysed the transcriptional regulation of the TPS2 gene and have shown that its transcription is induced by a variety of stressful conditions caused by metabolic inhibitors, osmotic shock and heat shock. This transcriptional activation is mediated by multiple stress promoter elements (C4T) and requires the function of Yap1p as well as reduced activity of the cAMP-regulated protein kinase. Using an appropriate reporter gene we have shown that Yap1p is generally required for transcriptional regulation through the C4T stress element. These results show that the YAP1 protein has a pivotal role in the metabolic stress response and the acquisition of stress tolerance.

Initial sequencing and analysis of the human genome.

Abstract: The human genome holds an extraordinary trove of information about human development, physiology, medicine and evolution. Here we report the results of an international collaboration to produce and make freely available a draft sequence of the human genome. We also present an initial analysis of the data, describing some of the insights that can be gleaned from the sequence.

The protein kinase family: conserved features and deduced phylogeny of the catalytic domains.

Abstract: In recent years, members of the protein kinase family have been discovered at an accelerated pace. Most were first described, not through the traditional biochemical approach of protein purification and enzyme assay, but as putative protein kinase amino acid sequences deduced from the nucleotide sequences of molecularly cloned genes or complementary DNAs. Phylogenetic mapping of the conserved protein kinase catalytic domains can serve as a useful first step in the functional characterization of these newly identified family members.

Life with 6000 Genes

Abstract: The genome of the yeast Saccharomyces cerevisiae has been completely sequenced through a worldwide collaboration. The sequence of 12,068 kilobases defines 5885 potential protein-encoding genes, approximately 140 genes specifying ribosomal RNA, 40 genes for small nuclear RNA molecules, and 275 transfer RNA genes. In addition, the complete sequence provides information about the higher order organization of yeast's 16 chromosomes and allows some insight into their evolutionary history. The genome shows a considerable amount of apparent genetic redundancy, and one of the major problems to be tackled during the next stage of the yeast genome project is to elucidate the biological functions of all of these genes.

Designer deletion strains derived from Saccharomyces cerevisiae S288C: a useful set of strains and plasmids for PCR-mediated gene disruption and other applications.

Abstract: A set of yeast strains based on Saccharomyces cerevisiae S288C in which commonly used selectable marker genes are deleted by design based on the yeast genome sequence has been constructed and analysed. These strains minimize or eliminate the homology to the corresponding marker genes in commonly used vectors without significantly affecting adjacent gene expression. Because the homology between commonly used auxotrophic marker gene segments and genomic sequences has been largely or completely abolished, these strains will also reduce plasmid integration events which can interfere with a wide variety of molecular genetic applications. We also report the construction of new members of the pRS400 series of vectors, containing the kanMX, ADE2 and MET15 genes.

The scanning model for translation: an update.

Abstract: The small (40S) subunit of eukaryotic ribosomes is believed to bind initially at the capped 5'-end of messenger RNA and then migrate, stopping at the first AUG codon in a favorable context for initiating translation. The first-AUG rule is not absolute, but there are rules for breaking the rule. Some anomalous observations that seemed to contradict the scanning mechanism now appear to be artifacts. A few genuine anomalies remain unexplained.