The Ashbya Genome Database (AGD)—a tool for the yeast community and genome biologists

The Ashbya Genome Database (AGD) is a comprehensive online source of information covering genes from the filamentous fungus Ashbya gossypii. The database content is based upon comparative genome annotation between A.gossypii and the closely related budding yeast Saccharomyces cerevisiae taking both sequence similarity and synteny (conserved order and orientation) into account. Release 2 of AGD contains 4718 protein-encoding loci located across seven chromosomes. Information can be retrieved using systematic or standard locus names from A.gossypii as well as budding and fission yeast. Approximately 90% of the genes in the genome of A.gossypii are homologous and syntenic to loci of budding yeast. Therefore, AGD is a useful tool not only for the various yeast communities in general but also for biologists who are interested in evolutionary aspects of genome research and comparative genome annotation. The database provides scientists with a convenient graphical user interface that includes various locus search and genome browsing options, data download and export functionalities and numerous reciprocal links to external databases including SGD, MIPS, GeneDB, KEGG, GermOnline and Swiss-Prot/TrEMBL. AGD is accessible at http://agd.unibas.c

Determinants of the temperature adaptation of mRNA degradation

The rate of chemical reactions increases proportionally with temperature, but the interplay of biochemical reactions permits deviations from this relation and adaptation. The degradation of individual mRNAs in yeast increased to varying degrees with temperature. We examined how these variations are influenced by the translation and codon composition of mRNAs. We developed a method that revealed the existence of a neutral half-life above which mRNAs are stabilized by translation but below which they are destabilized. The proportion of these two mRNA subpopulations remained relatively constant under different conditions, even with slow cell growth due to nutrient limitation, but heat shock reduced the proportion of translationally stabilized mRNAs. At the same time, the degradation of these mRNAs was partially temperature-compensated through Upf1, the mediator of nonsense-mediated decay. Compensation was also promoted by some asparagine and serine codons, whereas tyrosine codons promote temperature sensitization. These codons play an important role in the degradation of mRNAs encoding key cell membrane and cell wall proteins, which promote cell integrity

Ashbya Genome Database 3.0: a cross-species genome and transcriptome browser for yeast biologists

BACKGROUND: The Ashbya Genome Database (AGD) 3.0 is an innovative cross-species genome and transcriptome browser based on release 40 of the Ensembl developer environment. DESCRIPTION: AGD 3.0 provides information on 4726 protein-encoding loci and 293 non-coding RNA genes present in the genome of the filamentous fungus Ashbya gossypii. A synteny viewer depicts the chromosomal location and orientation of orthologous genes in the budding yeast Saccharomyces cerevisiae. Genome-wide expression profiling data obtained with high-density oligonucleotide microarrays (GeneChips) are available for nearly all currently annotated protein-coding loci in A. gossypii and S. cerevisiae. CONCLUSION: AGD 3.0 hence provides yeast- and genome biologists with comprehensive report pages including reliable DNA annotation, Gene Ontology terms associated with S. cerevisiae orthologues and RNA expression data as well as numerous links to external sources of information. The database is accessible at

Multiplexed gene control reveals rapid mRNA turnover

The rates of mRNA synthesis and decay determine the mRNA expression level. The two processes are under coordinated control, which makes the measurements of these rates challenging, as evidenced by the low correlation among the methods of measurement of RNA half-lives. We developed a minimally invasive method, multiplexed gene control, to shut off expression of genes with controllable synthetic promoters. The method was validated by measuring the ratios of the nascent to mature mRNA molecules and by measuring the half-life with endogenous promoters that can be controlled naturally or through inserting short sequences that impart repressibility. The measured mRNA half-lives correlated highly with those obtained with the metabolic pulse-labeling method in yeast. However, mRNA degradation was considerably faster in comparison to previous estimates, with a median half-life of around 2 min. The half-life permits the estimation of promoter-dependent and promoter-independent transcription rates. The dynamical range of the promoter-independent transcription rates was larger than that of the mRNA half-lives. The rapid mRNA turnover and the broad adjustability of promoter-independent transcription rates are expected to have a major impact on stochastic gene expression and gene network behavior

Reinvestigation of the Saccharomyces cerevisiae genome annotation by comparison to the genome of a related fungus: Ashbya gossypii

BACKGROUND: The recently sequenced genome of the filamentous fungus Ashbya gossypii revealed remarkable similarities to that of the budding yeast Saccharomyces cerevisiae both at the level of homology and synteny (conservation of gene order). Thus, it became possible to reinvestigate the S. cerevisiae genome in the syntenic regions leading to an improved annotation. RESULTS: We have identified 23 novel S. cerevisiae open reading frames (ORFs) as syntenic homologs of A. gossypii genes; for all but one, homologs are present in other eukaryotes including humans. Other comparisons identified 13 overlooked introns and suggested 69 potential sequence corrections resulting in ORF extensions or ORF fusions with improved homology to the syntenic A. gossypii homologs. Of the proposed corrections, 25 were tested and confirmed by resequencing. In addition, homologs of nearly 1,000 S. cerevisiae ORFs, presently annotated as hypothetical, were found in A. gossypii at syntenic positions and can therefore be considered as authentic genes. Finally, we suggest that over 400 S. cerevisiae ORFs that overlap other ORFs in S. cerevisiae and for which no homolog can be detected in A. gossypii should be regarded as spurious. CONCLUSIONS: Although, the S. cerevisiae genome is rightly considered as one of the most accurately sequenced and annotated eukaryotic genomes, we have shown that it still benefits substantially from comparison to the completed sequence and syntenic gene map of A. gossypii, an evolutionarily related fungus. This type of approach will strongly support the annotation of more complex genomes such as the human and murine genomes

Quantification of pre-mRNA escape rate and synergy in splicing

Splicing reactions generally combine high speed with accuracy. However, some of the pre-mRNAs escape the nucleus with a retained intron. Intron retention can control gene expression and increase proteome diversity. We calculated the escape rate for the yeast PTC7 intron and pre-mRNA. This prediction was facilitated by the observation that splicing is a linear process and by deriving simple algebraic expressions from a model of co- and post-transcriptional splicing and RNA surveillance that determines the rate of the nonsense-mediated decay (NMD) of the pre-mRNAs with the retained intron. The escape rate was consistent with the observed threshold of splicing rate below which the mature mRNA level declined. When an mRNA contains multiple introns, the outcome of splicing becomes more difficult to predict since not only the escape rate of the pre-mRNA has to be considered, but also the possibility that the splicing of each intron is influenced by the others. We showed that the two adjacent introns in the SUS1 mRNA are spliced cooperatively, but this does not counteract the escape of the partially spliced mRNA. These findings will help to infer promoter activity and to predict the behavior of and to control splicing regulatory networks

Contribution of RNA Degradation to Intrinsic and Extrinsic Noise in Gene Expression

Summary: Genetically identical cells contain variable numbers of molecules, even if the cells share the same environment. This stochastic variability is prominent when molecules have low abundance, which is the case for mRNA noise. Most studies focused on how transcription affects mRNA noise, and little is known about the role of RNA degradation. To discriminate the fluctuations in these processes during the decay of a pair of reporter mRNAs, we quantified the uncorrelated intrinsic and the correlated extrinsic noise using single-molecule RNA FISH. Intrinsic noise converges to the Poisson level during the decay. mRNAs that have a short half-life are more susceptible to extrinsic noise than stable mRNAs. However, the Xrn1 exonuclease and the NMD pathways, which degrade mRNAs rapidly, were found to have lower fluctuation, which mitigates the noise of the short-lived mRNAs. This permits low variability across the entire range of mRNA half-lives. : Baudrimont et al. show that fluctuations in transcription and RNA degradation can be distinguished by assessing whether extrinsic noise increases during decay. Unstable RNAs are more susceptible to noise, but the activity of the enzymes that degrade them fluctuates less in comparison to those that target stable mRNAs. Keywords: Saccharomyces cerevisiae, gene expression noise, single-molecule RNA FISH, surveillance pathway, birth-death model, exosome, RNA stability, galactose, stochastic deviatio