| 1. |
- Antoun, Ayman, et al.
(författare)
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How initiation factors maximize the accuracy of tRNA selection in initiation of bacterial protein synthesis
- 2006
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Ingår i: Molecular Cell. - : Elsevier BV. - 1097-2765 .- 1097-4164. ; 23:2, s. 183-193
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Tidskriftsartikel (refereegranskat)abstract
- During initiation of bacterial protein synthesis, messenger RNA and fMet-tRNA(fMet) bind to the 30S ribosomal subunit together with initiation factors IF1, IF2, and IF3. Docking of the 30S preinitiation complex to the 50S ribosomal subunit results in a peptidyl-transfer competent 70S ribosome. Initiation with an elongator tRNA may lead to frameshift and an aberrant N-terminal sequence in the nascent protein. We show how the occurrence of initiation errors is minimized by (1) recognition of the formyl group by the synergistic action of IF2 and IF1, (2) uniform destabilization of the binding of all tRNAs to the 30S subunit by IF3, and (3) an optimal distance between the Shine-Dalgarno sequence and the initiator codon. We suggest why IF1 is essential for E. coli, discuss the role of the G-C base pairs in the anticodon stem of some tRNAs, and clarify gene expression changes with varying IF3 concentration in the living cell.
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| 2. |
- Darfeuille, Fabien, et al.
(författare)
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An antisense RNA inhibits translation by competing with standby ribosomes
- 2007
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Ingår i: Molecular Cell. - : Elsevier BV. - 1097-2765 .- 1097-4164. ; 26:3, s. 381-392
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Tidskriftsartikel (refereegranskat)abstract
- Most antisense RNAs in bacteria inhibit translation by competing with ribosomes for translation initiation regions (TIRs) on nascent mRNA. We propose a mechanism by which an antisense RNA inhibits translation without binding directly to a TIR. The tisAB locus encodes an SOS-induced toxin, and IstR-1 is the antisense RNA that counteracts toxicity. We show that full-length tisAB mRNA (+1) is translationally inactive and endonucleolytic processing produces an active mRNA (+42). IstR-1 binding inhibits translation of this mRNA, and subsequent RNase III cleavage generates a truncated, inactive mRNA (+106). In vitro translation, toeprinting, and structure mapping suggest that active, but not inactive, tisAB mRNAs contain an upstream ribosome loading or “standby” site. Standby binding is required for initiation at the highly structured tisB TIR. This may involve ribosome sliding to a transiently open tisB TIR. IstR-1 competes with ribosomes by base pairing to the standby site located 100 nucleotides upstream.
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| 3. |
- Gaullier, Guillaume, et al.
(författare)
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PARP1 and Sox2 : An Unlikely Team of Pioneers to Conquer the Nucleosome.
- 2017
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Ingår i: Molecular Cell. - : Elsevier BV. - 1097-2765 .- 1097-4164. ; 65:4, s. 581-582
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Tidskriftsartikel (refereegranskat)abstract
- In this issue of Molecular Cell, Liu and Kraus (2017) demonstrate that the pioneer transcription factor Sox2 requires PARP1 to bind to a subset of its recognition motifs, which are located within nucleosomes across the genome.
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| 4. |
- Grönroos, Eva, et al.
(författare)
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Control of Smad7 stability by competition between acetylation and ubiquitination
- 2002
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Ingår i: Molecular Cell. - 1097-2765 .- 1097-4164. ; 10:3, s. 483-493
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Tidskriftsartikel (refereegranskat)abstract
- Smad proteins regulate gene expression in response to TGFbeta signaling. Here we present evidence that Smad7 interacts with the transcriptional coactivator p300, resulting in acetylation of Smad7 on two lysine residues in its N terminus. Acetylation or mutation of these lysine residues stabilizes Smad7 and protects it from TGFbeta-induced degradation. Furthermore, we demonstrate that the acetylated residues in Smad7 also are targeted by ubiquitination and that acetylation of these lysine residues prevents subsequent ubiquitination. Specifically, acetylation of Smad7 protects it against ubiquitination and degradation mediated by the ubiquitin ligase Smurf1. Thus, our data suggest that competition between ubiquitination and acetylation of overlapping lysine residues constitutes a novel mechanism to regulate protein stability.
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| 5. |
- Hewitt, Graeme, et al.
(författare)
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Defective ALC1 nucleosome remodeling confers PARPi sensitization and synthetic lethality with HRD
- 2021
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Ingår i: Molecular Cell. - : Cell Press. - 1097-2765 .- 1097-4164. ; 81:4, s. 767-783.e11
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Tidskriftsartikel (refereegranskat)abstract
- Chromatin is a barrier to efficient DNA repair, as it hinders access and processing of certain DNA lesions. ALC1/CHD1L is a nucleosome-remodeling enzyme that responds to DNA damage, but its precise function in DNA repair remains unknown. Here we report that loss of ALC1 confers sensitivity to PARP inhibitors, methyl-methanesulfonate, and uracil misincorporation, which reflects the need to remodel nucleosomes following base excision by DNA glycosylases but prior to handover to APEX1. Using CRISPR screens, we establish that ALC1 loss is synthetic lethal with homologous recombination deficiency (HRD), which we attribute to chromosome instability caused by unrepaired DNA gaps at replication forks. In the absence of ALC1 or APEX1, incomplete processing of BER intermediates results in post-replicative DNA gaps and a critical dependence on HR for repair. Hence, targeting ALC1 alone or as a PARP inhibitor sensitizer could be employed to augment existing therapeutic strategies for HRD cancers.
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| 6. |
- Holmqvist, Erik, 1977-, et al.
(författare)
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Global Maps of ProQ Binding In Vivo Reveal Target Recognition via RNA Structure and Stability Control at mRNA 3 ' Ends
- 2018
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Ingår i: Molecular Cell. - : CELL PRESS. - 1097-2765 .- 1097-4164. ; 70:5, s. 971-982
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Tidskriftsartikel (refereegranskat)abstract
- The conserved RNA-binding protein ProQ has emerged as the centerpiece of a previously unknown third large network of post-transcriptional control in enterobacteria. Here, we have used in vivo UV cross-linking and RNA sequencing (CLIP-seq) to map hundreds of ProQ binding sites in Salmonella enterica and Escherichia coli. Our analysis of these binding sites, many of which are conserved, suggests that ProQ recognizes its cellular targets through RNA structural motifs found in small RNAs (sRNAs) and at the 3' end of mRNAs. Using the cspE mRNA as a model for 3' end targeting, we reveal a function for ProQ in protecting mRNA against exoribonucleolytic activity. Taken together, our results underpin the notion that ProQ governs a post-transcriptional network distinct from those of the well-characterized sRNA-binding proteins, CsrA and Hfq, and suggest a previously unrecognized, sRNA-independent role of ProQ in stabilizing mRNAs.
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| 7. |
- Johansson, Magnus, et al.
(författare)
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The kinetics of ribosomal peptidyl transfer revisited
- 2008
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Ingår i: Molecular Cell. - : Elsevier BV. - 1097-2765 .- 1097-4164. ; 30:5, s. 589-598
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Tidskriftsartikel (refereegranskat)abstract
- The speed of protein synthesis determines the growth rate of bacteria. Current biochemical estimates of the rate of protein elongation are small and incompatible with the rate of protein elongation in the living cell. With a cell-free system for protein synthesis, optimized for speed and accuracy, we have estimated the rate of peptidyl transfer from a peptidyl-tRNA in P site to a cognate aminoacyl-tRNA in A site at various temperatures. We have found these rates to be much larger than previously measured and fully compatible with the speed of protein elongation for E. coli cells growing in rich medium. We have found large activation enthalpy and small activation entropy for peptidyl transfer, similar to experimental estimates of these parameters for A site analogs of aminoacyl-tRNA. Our work has opened a useful kinetic window for biochemical studies of protein synthesis, bridging the gap between in vitro and in vivo data on ribosome function.
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| 8. |
- Lehmann, Laura C., et al.
(författare)
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Mechanistic Insights into Autoinhibition of the Oncogenic Chromatin Remodeler ALC1
- 2017
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Ingår i: Molecular Cell. - : Elsevier BV. - 1097-2765 .- 1097-4164. ; 68:5, s. 847-859 (e7)
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Tidskriftsartikel (refereegranskat)abstract
- Human ALC1 is an oncogene-encoded chromatin-remodeling enzyme required for DNA repair that possesses a poly(ADP-ribose) (PAR)-binding macro domain. Its engagement with PARylated PARP1 activates ALC1 at sites of DNA damage, but the underlying-mechanism remains unclear. Here, we establish a dual role for the macro domain in autoinhibition of ALC1 ATPase activity and coupling to nucleosome mobilization. In the absence of DNA damage, an inactive conformation of the ATPase is maintained by juxtaposition of the macro domain against predominantly the C-terminal ATPase lobe through conserved electrostatic interactions. Mutations within this interface displace the macro domain, constitutively activate the ALC1 ATPase independent of PARylated PARP1, and alter the dynamics of ALC1 recruitment at DNA damage sites. Upon DNA damage, binding of PARylated PARP1 by the macro domain induces a conformational change that relieves autoinhibitory interactions with the ATPase motor, which selectively activates ALC1 remodeling upon recruitment to sites of DNA damage.
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| 9. |
- Levine, Daniel C., et al.
(författare)
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NAD+ Controls Circadian Reprogramming through PER2 Nuclear Translocation to Counter Aging
- 2020
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Ingår i: Molecular Cell. - : Elsevier BV. - 1097-2765 .- 1097-4164. ; 78:5, s. 835-
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Tidskriftsartikel (refereegranskat)abstract
- Disrupted sleep-wake and molecular circadian rhythms are a feature of aging associated with metabolic disease and reduced levels of NAD(+), yet whether changes in nucleotide metabolism control circadian behavioral and genomic rhythms remains unknown. Here, we reveal that supplementation with the NAD(+) precursor nicotinamide riboside (NR) markedly reprograms metabolic and stress-response pathways that decline with aging through inhibition of the clock repressor PER2. NR enhances BMAL1 chromatin binding genome-wide through PER2K680 deacetylation, which in turn primes PER2 phosphorylation within a domain that controls nuclear transport and stability and that is mutated in human advanced sleep phase syndrome. In old mice, dampened BMAL1 chromatin binding, transcriptional oscillations, mitochondrial respiration rhythms, and late evening activity are restored by NAD(+) repletion to youthful levels with NR. These results reveal effects of NAD(+) on metabolism and the circadian system with aging through the spatiotemporal control of the molecular clock.
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| 10. |
- Lönn, Peter, et al.
(författare)
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PARP-1 attenuates Smad-mediated transcription
- 2010
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Ingår i: Molecular Cell. - : Elsevier BV. - 1097-2765 .- 1097-4164. ; 40:4, s. 521-532
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Tidskriftsartikel (refereegranskat)abstract
- The versatile cytokine transforming growth factor β (TGF-β) regulates cellular growth, differentiation, and migration during embryonic development and adult tissue homeostasis. Activation of TGF-β receptors leads to phosphorylation of Smad2 and Smad3, which oligomerize with Smad4 and accumulate in the nucleus where they recognize gene regulatory regions and orchestrate transcription. Termination of Smad-activated transcription involves Smad dephosphorylation, nuclear export, or ubiquitin-mediated degradation. In an unbiased proteomic screen, we identified poly(ADP-ribose) polymerase-1 (PARP-1) as a Smad-interacting partner. PARP-1 dissociates Smad complexes from DNA by ADP-ribosylating Smad3 and Smad4, which attenuates Smad-specific gene responses and TGF-β-induced epithelial-mesenchymal transition. Thus, our results identify ADP-ribosylation of Smad proteins by PARP-1 as a key step in controlling the strength and duration of Smad-mediated transcription.
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