| 1. |
- Balciunas, Darius, et al.
(författare)
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The Med1 subunit of the yeast mediator complex is involved in both transcriptional activation and repression
- 1999
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Ingår i: Proceedings of the National Academy of Sciences of the United States of America. - : Proceedings of the National Academy of Sciences (PNAS). - 0027-8424 .- 1091-6490. ; 96:2, s. 376-381
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Tidskriftsartikel (refereegranskat)abstract
- The mediator complex is essential for regulated transcription in vitro. In the yeast Saccharomyces cerevisiae, mediator comprises >15 subunits and interacts with the C-terminal domain of the largest subunit of RNA polymerase II, thus forming an RNA polymerase II holoenzyme. Here we describe the molecular cloning of the MED1 cDNA encoding the 70-kDa subunit of the mediator complex. Yeast cells lacking the MED1 gene are viable but show a complex phenotype including partial defects in both repression and induction of the GAL genes. Together with results on other mediator subunits, this implies that the mediator is involved in both transcriptional activation and repression. Similar to mutations in the SRB10 and SRB11 genes encoding cyclin C and the cyclin C-dependent kinase, a disruption of the MED1 gene can partially suppress loss of the Snf1 protein kinase. We further found that a lexA-Med1 fusion protein is a strong activator in srb11 cells, which suggests a functional link between Med1 and the Srb10/11 complex. Finally, we show that the Med2 protein is lost from the mediator on purification from Med1-deficient cells, indicating a physical interaction between Med1 and Med2.
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| 2. |
- Björklund, Stefan, et al.
(författare)
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An S-phase specific release from a transcriptional block regulates the expression of mouse ribonucleotide reductase R2 subunit
- 1992
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Ingår i: EMBO Journal. - 0261-4189 .- 1460-2075. ; 11:13, s. 4953-4959
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Tidskriftsartikel (refereegranskat)abstract
- Ribonucleotide reductase (RR) activity in mammalian cells is closely linked to DNA synthesis. The RR enzyme is composed of two non-identical subunits, proteins R1 and R2. Both proteins are required for holoenzyme activity, which is regulated by S-phase specific de novo synthesis and breakdown of the R2 subunit. In quiescent cells stimulated to proliferate and in elutriated cell populations enriched in the various cell cycle phases the R2 protein levels are correlated to R2 mRNA levels that are low in G0/G1-phase cells but increase dramatically at the G1/S border. Using an R2 promoter-luciferase reporter gene construct we demonstrate an unexpected early activation of the R2 promoter as cells pass from quiescence to proliferation. However, due to a transcriptional block, this promoter activation only results in very short R2 transcripts until cells enter the S-phase, when full-length R2 transcripts start to appear. The position for the transcriptional block was localized to a nucleotide sequence approximately 87 bp downstream from the first exon/intron boundary by S1 nuclease mapping of R2 transcripts from modified in vitro nuclear run-on experiments. These results identify blocking of transcription as a mechanism to control cell cycle regulated gene expression.
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| 3. |
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| 4. |
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| 5. |
- Björklund, Stefan, et al.
(författare)
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Mediator of transcriptional regulation.
- 1996
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Ingår i: TIBS -Trends in Biochemical Sciences. Regular ed.. - 0968-0004 .- 1362-4326. ; 21:9, s. 335-7
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Tidskriftsartikel (refereegranskat)abstract
- A multi-protein complex, termed mediator, has been isolated from yeast, based on its requirement for transcriptional activation in a system reconstituted from pure RNA polymerase II and general transcription factors. Mediator polypeptides include the products of many genes previously recovered from screens for mutations affecting transcription. This connection between biochemical and genetic studies reveals that mediator is important for both activation and repression of transcription, and that mediator plays a role in transcriptional regulation in vivo as well as in vitro. Mediator binds the carboxy-terminal domain of RNA polymerase II, forming a polymerase holoenzyme, whose possible association with additional proteins is a subject of some controversy.
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| 6. |
- Björklund, Stefan, et al.
(författare)
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S-phase-specific expression of mammalian ribonucleotide reductase R1 and R2 subunit mRNAs
- 1990
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Ingår i: Biochemistry. - : American Chemical Society (ACS). - 0006-2960 .- 1520-4995. ; 29:23, s. 5452-5458
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Tidskriftsartikel (refereegranskat)abstract
- Ribonucleotide reductase in mammalian cells is composed of two nonidentical subunits, proteins R1 and R2, each inactive alone. The R1 protein is present in excess in proliferating cells, and its levels are constant during the cell cycle. Expression of the R2 protein, which is limiting for enzyme activity, is strictly S-phase-correlated. In this paper, we have used antisense RNA probes in a solution hybridization assay to measure the levels of R1 and R2 mRNA during the cell cycle in centrifugally elutriated cells and in cells synchronized by isoleucine or serum starvation. The levels of both transcripts were very low or undetectable in G0/G1-phase cells, showed a pronounced increase as cells progressed into S phase, and then declined when cells progressed into G2 + M phase. The R1 and R2 transcripts increased in parallel, starting slightly before the rise in S-phase cells, and reached the same levels. The relative lack of cell cycle dependent variation in R1 protein levels, obtained previously, may therefore simply be a consequence of the long half-life of the R1 protein. Hydroxyurea-resistant, R2-overproducing mouse TA3 cells showed the same regulation of the R1 and R2 transcripts as the parental cells, but with R2 mRNA at a 40-fold higher level.
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| 9. |
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| 10. |
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| 11. |
- Kim, Y J, et al.
(författare)
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A multiprotein mediator of transcriptional activation and its interaction with the C-terminal repeat domain of RNA polymerase II.
- 1994
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Ingår i: Cell. - 0092-8674 .- 1097-4172. ; 77:4, s. 599-608
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Tidskriftsartikel (refereegranskat)abstract
- A mediator was isolated from yeast that enabled a response to the activator proteins GAL4-VP16 and GCN4 in a transcription system reconstituted with essentially homogeneous basal factors and RNA polymerase II. The mediator comprised some 20 polypeptides, including the three subunits of TFIIF and other polypeptides cross-reactive with antisera against GAL11, SUG1, SRB2, SRB4, SRB5, and SRB6 proteins. Mediator not only enabled activated transcription but also conferred 8-fold greater activity in basal transcription and 12-fold greater efficiency of phosphorylation of RNA polymerase II by the TFIIH-associated C-terminal repeat domain (CTD) kinase, indicative of mediator-CTD interaction. A holoenzyme form of RNA polymerase II was independently isolated that supported a response to activator proteins with purified basal factors. The holoenzyme proved to consist of mediator associated with core 12-subunit RNA polymerase II.
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| 12. |
- Sellgren, Ulf, et al.
(författare)
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A Contact Model for Rough Surfaces
- 1999
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Ingår i: NAFEMS World Congress, April 25-28 1999, Newport, Rhode Island,USA.
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Konferensbidrag (övrigt vetenskapligt/konstnärligt)abstract
- Engineering surfaces can be characterized as more or less randomly rough. Contact between engineering surfaces is thus discontinuous and the real area of contact is a small fraction of the nominal contact area. The stiffness of a rough surface layer will thus have an influence on the contact state as well as on the behavior of the surrounding system. A contact model that takes the properties of engineering surfaces into account has been developed and implemented in a commercial FE software. Results obtained with the model have been compared and verified with results from an independent numerical method. Results have shown that the height distribution of the topography has a significant influence on the contact stiffness but that the curvature of the roughness is of minor importance. The contact model that was developed for determining the apparent contact area and the distribution of the mean contact pressure could thus be based on a limited set of height parameters that describe the surface topography. By operating on the calculated apparent pressure distribution with a transformation function that is based on both height and curvature parameters, the real contact area can be estimated in a post processing step.
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