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- Mannervik, Mattias, et al.
(författare)
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Adenovirus E4 open reading frame 4-induced dephosphorylation inhibits E1A activation of the E2 promoter and E2F-1-mediated transactivation independently of the retinoblastoma tumor suppressor protein
- 1999
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Ingår i: Virology. - : Elsevier BV. - 0042-6822 .- 1096-0341. ; 256:2, s. 313-321
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Tidskriftsartikel (refereegranskat)abstract
- Previous studies have shown that the cell cycle-regulated E2F transcription factor is subjected to both positive and negative control by phosphorylation. Here we show that in transient transfection experiments, adenovirus E1A activation of the viral E2 promoter is abrogated by coexpression of the viral E4 open reading frame 4 (E4-ORF4) protein. This effect does not to require the retinoblastoma protein that previously has been shown to regulate E2F activity. The inhibitory activity of E4-ORF4 appears to be specific because E4-ORF4 had little effect on, for example, E4-ORF6/7 transactivation of the E2 promoter. We further show that the repressive effect of E4-ORF4 on E2 transcription works mainly through the E2F DNA-binding sites in the E2 promoter. In agreement with this, we find that E4-ORF4 inhibits E2F-1/DP-1-mediated transactivation. We also show that E4-ORF4 inhibits E2 mRNA expression during virus growth. E4-ORF4 has previously been shown to bind to and activate the cellular protein phosphatase 2A. The inhibitory effect of E4-ORF4 was relieved by okadaic acid, which inhibits protein phosphatase 2A activity, suggesting that E4-ORF4 represses E2 transcription by inducing transcription factor dephosphorylation. Interestingly, E4-ORF4 did not inhibit the transactivation capacity of a Gal4-E2F hybrid protein. Instead, E4-ORF4 expression appears to result in reduced stability of E2F/DNA complexes.
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- Ström, Anne-Christine, et al.
(författare)
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The transcription factors Sp1 and Oct-1 interact physically to regulate human U2 snRNA gene expression
- 1996
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Ingår i: Nucleic Acids Research. - : Oxford University Press (OUP). - 0305-1048 .- 1362-4962. ; 24:11, s. 1981-1986
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Tidskriftsartikel (refereegranskat)abstract
- The expression of human small nuclear U2 RNA genes is controlled by the proximal sequence element (PSE), which determines the start site of transcription, and a distal sequence element (DSE). The DSE contains an octamer element and three Sp1 binding sites. The octamer, like the PSE, is essential for U2 transcription. The Sp1 sites contribute to full promoter activity by distance-dependent cooperative interactions with the transcription factors Sp1 and Oct-1. Here we show that purified recombinant Sp1 and Oct-1 bind cooperatively to the DSE and that they physically interact in vitro. Furthermore, we show that Sp1 and Oct-1 interact in vivo using a yeast two-hybrid system. The domain of Sp1 which interacts with Oct-1 is confined to the region necessary for transcriptional stimulation of U2 RNA transcription. This region contains the glutamine-rich activation domain B and a serine/threonine-rich part. The results demonstrate that Sp1, in addition to binding to a number of other factors, also interacts directly with transcription factor Oct-1.
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| 5. |
- Ström, Anne-Christine
(författare)
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Transcriptional activation by Sp1 and the adenovirus E1A transactivator protein
- 1998
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Transcription is a key step in the regulation of gene expression. Activation of transcriptionrequires that the RNA polymerase receive both, regulatory signals from transcription factors,and initiate transcription at the correct location in the genome, at the promoter. A key issuedescribed in this thesis is the understanding of how transcription factors function to achievethe specificity required to regulate the complex pattern of gene expression. In particular,transcriptional regulation by the human Sp1 factor and the adenovirus encoded E1A proteinhave been studied.Sp1 is a ubiquitously expressed human transcription factor which regulatestranscription of several genes by synergistically interacting with a variety of transcriptionfactors, coactivators and TAFs. This thesis addresses whether Sp1 requires different regions,to mediate activation from two different RNA polymerase II promoters. Genetic studiesrevealed that overlapping but not identical parts of Sp1 were required for stimulation of aTATA box containing promoter and a U2 snRNA promoter. Moreover, this work describes the nature of the cooperativity between the transcription factors Sp1 and Oct-l. These factorswere found to cooperatively bind the U2 enhancer, as well as psychically interact, both in astandard in vitro binding approach, and in the yeast two hybrid system in vivo. The part ofSpl that bound to Oct-1 was found be located in a region necessary for transcriptionalstimulation of U2 transcription. Since there was a correlation between the in vitro interaction and the in vivo transcriptional activation, these results suggest that the physical interaction between these factors is of functional importance.Adenoviruses are small DNA viruses that use the mammalian transcriptionalmachinery to activate transcription of their own genes. This thesis describes the structuralfeatures of a novel region, termed auxiliary region 1 (AR1), located in the adenovirus encodedE1A protein. Genetic dissection of the AR1 region revealed, that E1A mediatedtranscriptional activation required the AR1 element in addition to the classicaltransactivation domain (CR3) for efficient activation of all early viral adenovirus promoters.Since the AR1 region is an essential element for viral transcription and located next to theCR3 region, this thesis suggest that the CR3 activation domain should be extended to alsoinclude AR1.
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