Eva Murén

Combinatorial control of gene expression by the three yeast repressors Mig1, Mig2 and Mig3

BackgroundExpression of a large number of yeast genes is repressed by glucose. The zinc finger protein Mig1 is the main effector in glucose repression, but yeast also has two related proteins: Mig2 and Mig3. We have used microarrays to study global gene expression in all possible combinations of mig1, mig2 and mig3 deletion mutants.ResultsMig1 and Mig2 repress a largely overlapping set of genes on 2% glucose. Genes that are upregulated in a mig1 mig2 double mutant were grouped according to the contribution of Mig2. Most of them show partially redundant repression, with Mig1 being the major repressor, but some genes show complete redundancy, and some are repressed only by Mig1. Several redundantly repressed genes are involved in phosphate metabolism. The promoters of these genes are enriched for Pho4 sites, a novel GGGAGG motif, and a variant Mig1 site which is absent from genes repressed only by Mig1. Genes repressed only by Mig1 on 2% glucose include the hexose transporter gene HXT4, but Mig2 contributes to HXT4 repression on 10% glucose. HXT6 is one of the few genes that are more strongly repressed by Mig2. Mig3 does not seem to overlap in function with Mig1 and Mig2. Instead, Mig3 downregulates the SIR2 gene encoding a histone deacetylase involved in gene silencing and the control of aging.ConclusionMig2 fine-tunes glucose repression by targeting a subset of the Mig1-repressed genes, and by responding to higher glucose concentrations. Mig3 does not target the same genes as Mig1 and Mig2, but instead downregulates the SIR2 gene.

The jmjN and jmjC domains of the yeast zinc finger protein Gis1 interact with 19 proteins involved in transcription, sumoylation and DNA repair.

The jumonji domain is a highly conserved bipartite domain made up of two subdomains, jmjN and jmjC, which is found in many eukaryotic transcription factors. The jmjC domain was recently shown to possess the histone demethylase activity. Here we show that the jmjN and jmjC domains of the yeast zinc finger protein Gis1 interact in a two-hybrid system with 19 yeast proteins that include the RecQ helicase Sgs1, the silencing factors Esc1 and Sir4, the URI-type prefoldin Bud27 and the PIAS type SUMO ligase Nfi1/Siz2. Extensive interaction cross dependencies further suggest that the proteins form a larger complex. Consistent with this, 16 of the proteins also interact with a Bud27 two-hybrid bait, and three of them co-precipitate with TAP-tagged Gis1. The Gis1 jumonji domain can repress transcription when recruited to a promoter as a lexA fusion. This effect is dependent on both the jmjN and jmjC subdomains, as were all 19 two-hybrid interactions, indicating that the two subdomains form a single functional unit. The human Sgs1 homolog WRN also interacts with the Gis1 jumonji domain. Finally, we note that several jumonji domain interactors are related to proteins that are found in mammalian PML nuclear bodies.

Functional genomics of monensin sensitivity in yeast: implications for post-Golgi traffic and vacuolar H+-ATPase function

We have screened a complete collection of yeast knockout mutants for sensitivity to monensin, an ionophore that interferes with intracellular transport. A total of 63 sensitive strains were found. Most of the strains were deleted for genes involved in post-Golgi traffic, with an emphasis on vacuolar biogenesis. A high correlation was thus seen with VPS and VAM genes, but there were also significant differences between the three sets of genes. A weaker correlation was seen with sensitivity to NaCl, in particular rate of growth effects. Interestingly, all 14 genes encoding subunits of the vacuolar H+-ATPase (V-ATPase) were absent in our screen, even though they appeared in the VPS or VAM screens. All monensin-sensitive mutants that could be tested interact synthetically with a deletion of the A subunit of the V-ATPase, Vma1. Synthetic lethality was limited to mutations affecting endocytosis or retrograde transport to Golgi. In addition, vma1 was epistatic over the monensin sensitivity of vacuolar transport mutants, but not endocytosis mutants. Deletions of the two isoforms of the V-ATPase a subunit, Vph1 and Stv1 had opposite effects on the monensin sensitivity of a ypt7 mutant. These findings are consistent with a model where monensin inhibits growth by interfering with the maintenance of an acidic pH in the late secretory pathway. The synthetic lethality of vma1 with mutations affecting retrograde transport to the Golgi further suggests that it is in the late Golgi that a low pH must be maintained.

Rescue and characterization of episomally replicating DNA from the moss Physcomitrella

The moss Physcomitrella is unique among plants in that it permits efficient gene targeting by homologous recombination. Furthermore, transformed DNA can replicate episomally in Physcomitrella. Here we show that episomally replicating DNA can be rescued back into Escherichia coli, and we use such rescue to study the fate of the transformed DNA. Significantly, plasmids rescued from moss transformed with circular DNA are identical to the original plasmid, whereas plasmids rescued from moss transformed with linearized DNA frequently have deletions created by direct repeat recombination. These events are highly predictable in that they target the longest direct repeat on the plasmid if this repeat is at least 12 bp. Episomal transformants obtained with linearized DNA show a more than 1,000-fold amplification of the DNA whereas transformants obtained with circular DNA have much lower copy numbers. Most episomal transformants quickly lose the plasmid in the absence of selection, but a semistable type of transformant that loses the plasmid at a much lower frequency was also observed. The consistent rescue of the original plasmid, or of predictable derivatives thereof, suggests that molecular genetics methods which rely on shuttle plasmids are feasible in Physcomitrella.

Variants within the SP110 nuclear body protein modify risk of canine degenerative myelopathy

Significance Degenerative myelopathy (DM) is a canine disease very similar to amyotrophic lateral sclerosis (ALS) in humans. We previously showed that DM is a promising model for ALS, because genome-wide association identified a mutation in superoxide dismutase 1 gene (SOD1), a known ALS gene. This mutation found in many dog breeds increases the risk of DM, and the pathological findings and clinical progression of the two diseases are similar. In this study, we identify a modifier gene, SP110 nuclear body protein (SP110), which strongly affects overall disease risk and age of onset in Pembroke Welsh Corgis at risk for DM. Dissecting the complex genetics of this disease in a model organism may lead to new insights about risk and progression in both canine and human patients. Canine degenerative myelopathy (DM) is a naturally occurring neurodegenerative disease with similarities to some forms of amyotrophic lateral sclerosis (ALS). Most dogs that develop DM are homozygous for a common superoxide dismutase 1 gene (SOD1) mutation. However, not all dogs homozygous for this mutation develop disease. We performed a genome-wide association analysis in the Pembroke Welsh Corgi (PWC) breed comparing DM-affected and -unaffected dogs homozygous for the SOD1 mutation. The analysis revealed a modifier locus on canine chromosome 25. A haplotype within the SP110 nuclear body protein (SP110) was present in 40% of affected compared with 4% of unaffected dogs (P = 1.5 × 10−5), and was associated with increased probability of developing DM (P = 4.8 × 10−6) and earlier onset of disease (P = 1.7 × 10−5). SP110 is a nuclear body protein involved in the regulation of gene transcription. Our findings suggest that variations in SP110-mediated gene transcription may underlie, at least in part, the variability in risk for developing DM among PWCs that are homozygous for the disease-related SOD1 mutation. Further studies are warranted to clarify the effect of this modifier across dog breeds.

A Ham1p-Dependent Mechanism and Modulation of the Pyrimidine Biosynthetic Pathway Can Both Confer Resistance to 5-Fluorouracil in Yeast

5-Fluorouracil (5-FU) is an anticancer drug and pyrimidine analogue. A problem in 5-FU therapy is acquired resistance to the drug. To find out more about the mechanisms of resistance, we screened a plasmid library in yeast for genes that confer 5-FU resistance when overexpressed. We cloned five genes: CPA1, CPA2, HMS1, HAM1 and YJL055W. CPA1 and CPA2 encode a carbamoyl phosphate synthase involved in arginine biosynthesis and HMS1 a helix-loop-helix transcription factor. Our results suggest that CPA1, CPA2, and HMS1 confer 5-FU resistance by stimulating pyrimidine biosynthesis. Thus, they are unable to confer 5-FU resistance in a ura2 mutant, and inhibit the uptake and incorporation into RNA of both uracil and 5-FU. In contrast, HAM1 and YJL055W confer 5-FU resistance in a ura2 mutant, and selectively inhibit incorporation into RNA of 5-FU but not uracil. HAM1 is the strongest resistance gene, but it partially depends on YJL055W for its function. This suggests that HAM1 and YJL055W function together in mediating resistance to 5-FU. Ham1p encodes an inosine triphosphate pyrophosphatase that has been implicated in resistance to purine analogues. Our results suggest that Ham1p could have a broader specificity that includes 5-FUTP and other pyrimidine analogoue triphosphates.

Effects of growth conditions and mutations in RNA polymerase on translational activity in vitro in Escherichia coli

SummaryThe translational capacity in vitro in Escherichia coli, using RNA from phage R17 or Qβ as messenger, is several times higher if the extracts are prepared from cells harvested in early exponential phase or grown under conditions of good aeration compared to if extracts are prepared from cells harvested in a later growth phase or grown under semi-aerobic conditions. In low activity extracts the production of phage replicase protein is preferentially affected. Growth of a wild type strain under semiaerobic conditions has a less pronounced effect on translational capacity in vitro using crude mRNA from normal or T4 infected cells or with poly(U).Mutants were fortuitously found which did not show a lowered translational activity in vitro as a result of entering late phase of growth. Two of these were changed in RNA polymerase.Two different translational inhibitors can be demonstrated in the ribosomal wash fraction obtained from semi-aerobically grown wild type cells, whereas only one was found in the case of aerobically grown cells. The low translational activity of semi-aerobically grown cells in vitro is implied to be dependent on the induction or activation of a translational inhibitor. It behaves like a protein but is not likely to be a protease or RNAse.