Project description:Regulation of protein synthesis is fundamental for all aspects of eukaryotic biology by controlling development, homeostasis, and stress responses. The 13-subunit, 800-kDa eukaryotic initiation factor 3 (eIF3) organizes initiation factor and ribosome interactions required for productive translation. However, current understanding of eIF3 function does not explain genetic evidence correlating eIF3 deregulation with tissue-specific cancers and developmental defects. Here we report the genome-wide discovery of human transcripts that interact with eIF3 using photo-activatable crosslinking and immunoprecipitation (PAR-CLIP). eIF3 binds to a highly specific programme of messenger RNAs (mRNAs) involved in cell growth control processes, including cell cycling, differentiation, and apoptosis, via the mRNA 5' untranslated region (5' UTR). Surprisingly, functional analysis of the interaction between eIF3 and two mRNAs encoding cell proliferation regulators, c-Jun and BTG1, reveals that eIF3 employs different modes of RNA stem loop binding to exert either translational activation or repression. Our findings illuminate a new role for eIF3 in governing a specialized repertoire of gene expression and suggest that binding of eIF3 to specific mRNAs could be targeted to control carcinogenesis. 293T cells were treated with 4-thiouridine and protein-RNA complexes were crosslinked, and eIF3-RNA complexes were immunoprecipitated.
Project description:This is a part of the study that shows that a host microRNA, miR-138, represses herpes simplex virus 1 (HSV-1) gene expression through both viral and host targets. These PAR-CLIP analyses identified viral and host targets of miR-138 in Neuro-2a (mouse neuroblastoma) and 293T (human embryonic kidney) cells. We constructed two cell lines derived from Neuro-2a cells, one overexpressing miR-138 (N2A138) and one antagonizing miR-138 (N2Aanti138). We also constructed two cell lines derived from 293T cells, one overexpressing miR-138 (293T138) and one control cells (293Tcontrol). Uninfected N2A138 and N2Aanti138 were compared by PAR-CLIP for host targets in Neuro-2A cells. 293T138 and 293Tcontrol cells infected for 4 and 8 hours were compared by PAR-CLIP for HSV-1 targets in 293T cells. 293T138 and 293Tcontrol cells infected for 4 hours were also compared for host targets in 293T cells.
Project description:N6-methyladenosine (m6A) is a widespread internal RNA modification whose function is poorly understood. Here we report that m6A residues within the 5'UTR promote a novel form of cap-independent translation which is mediated through an interaction between m6A residues and the translation initiation factor, eIF3. We present eIF3a PAR-iCLIP data which demonstrate that eIF3 predominantly binds mRNAs within the 5'UTR. eIF3 binding sites are also in proximity to m6A residues within the 5'UTR of cellular mRNAs. Two replicates of eIF3a PAR-iCLIP in HEK293T cells.
Project description:Regulation of protein synthesis is fundamental for all aspects of eukaryotic biology by controlling development, homeostasis, and stress responses. The 13-subunit, 800-kDa eukaryotic initiation factor 3 (eIF3) organizes initiation factor and ribosome interactions required for productive translation. However, current understanding of eIF3 function does not explain genetic evidence correlating eIF3 deregulation with tissue-specific cancers and developmental defects. Here we report the genome-wide discovery of human transcripts that interact with eIF3 using photo-activatable crosslinking and immunoprecipitation (PAR-CLIP). eIF3 binds to a highly specific programme of messenger RNAs (mRNAs) involved in cell growth control processes, including cell cycling, differentiation, and apoptosis, via the mRNA 5' untranslated region (5' UTR). Surprisingly, functional analysis of the interaction between eIF3 and two mRNAs encoding cell proliferation regulators, c-Jun and BTG1, reveals that eIF3 employs different modes of RNA stem loop binding to exert either translational activation or repression. Our findings illuminate a new role for eIF3 in governing a specialized repertoire of gene expression and suggest that binding of eIF3 to specific mRNAs could be targeted to control carcinogenesis.
Project description:The identification of RNAs that are recognized by RNA-binding proteins (RNA-BPs) using techniques such as Crosslinking and Immunoprecipitation (CLIP) has revolutionized the genome-wide discovery of RNA-BP RNA targets. Among the different versions of CLIP that have been developed, the use of photoactivable nucleoside analogs has resulted in high efficiency photoactivable ribonucleoside-enhanced CLIP (PAR-CLIP) in vivo. Nonetheless, PAR-CLIP has not yet been applied in prokaryotes. To determine if PAR-CLIP can be used in prokaryotes, we determined suitable conditions for the incorporation of 4-thiouridine (4SU), a photoactivable nucleoside, into E. coli RNA and for the isolation of RNA crosslinked to RNA-BPs of interest. Applying this technique to Hfq, a well-characterized regulator of small RNA (sRNA)-messenger RNA (mRNA) interactions, we showed that PAR-CLIP identified most of the known sRNA targets of Hfq, as well as functionally relevant sites of Hfq-mRNA interactions at nucleotide resolution. Based on our findings, PAR-CLIP represents an improved method to identify both the RNAs and the specific regulatory sites that are recognized by RNA-BPs in prokaryotes.