Browsing by Subject "RNA-protein interactions"

Now showing 1 - 6 of 6
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    In silico λ-dynamics predicts protein binding specificities to modified RNAs
    (bioRxiv, 2024-01-27) Angelo, Murphy; Zhang, Wen; Vilseck, Jonah Z.; Aoki, Scott T.; Biochemistry and Molecular Biology, School of Medicine
    RNA modifications shape gene expression through a smorgasbord of chemical changes to canonical RNA bases. Although numbering in the hundreds, only a few RNA modifications are well characterized, in part due to the absence of methods to identify modification sites. Antibodies remain a common tool to identify modified RNA and infer modification sites through straightforward applications. However, specificity issues can result in off-target binding and confound conclusions. This work utilizes in silico λ-dynamics to efficiently estimate binding free energy differences of modification-targeting antibodies between a variety of naturally occurring RNA modifications. Crystal structures of inosine and N6-methyladenosine (m6A) targeting antibodies bound to their modified ribonucleosides were determined and served as structural starting points. λ-Dynamics was utilized to predict RNA modifications that permit or inhibit binding to these antibodies. In vitro RNA-antibody binding assays supported the accuracy of these in silico results. High agreement between experimental and computed binding propensities demonstrated that λ-dynamics can serve as a predictive screen for antibody specificity against libraries of RNA modifications. More importantly, this strategy is an innovative way to elucidate how hundreds of known RNA modifications interact with biological molecules without the limitations imposed by in vitro or in vivo methodologies.
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    Mechanisms of recruitment of the CTD phosphatase Rtr1 to RNA polymerase II
    (2012-10-19) Berna, Michael J., Sr.; Goebl, Mark G.; Mosley, Amber L.; Hurley, Thomas D., 1961-
    The C-terminal domain (CTD) of the RNA polymerase II (RNAPII) subunit Rpb1 must exist in a hypophosphorylated state prior to forming a competent transcription initiation complex. However, during transcription, specific kinases and phosphatases act on the RNAPII CTD to regulate its phosphorylation state, which serves to recruit sequence-specific and general transcription factors at the appropriate stage of transcription. A key phosphatase involved in this process, Rtr1 (Regulator of Transcription 1), was shown to regulate a key step important for transcription elongation and termination. Although the role that Rtr1 plays in regulating RNAPII transcription has been described, the mechanism involved in the recruitment of Rtr1 to RNAPII during transcription has not been elucidated in yeast. Consequently, the present work utilized both affinity purification schemes in Saccharomyces cerevisiae and mass spectrometry to identify key Rtr1-interacting proteins and post-translational modifications that potentially play a role in recruiting Rtr1 to RNAPII. In addition to RNAPII subunits, which were the most consistently enriched Rtr1-interacting proteins, seven proteins were identified that are potentially involved in Rtr1 recruitment. These included PAF complex subunits (Cdc73, Ctr9, Leo1), the heat shock protein Hsc82, the GTPase Npa3, the ATPase Rpt6, and Spn1. Indirect evidence was also uncovered that implicates that the CTDK-I complex, a kinase involved in RNAPII CTD phosphorylation, is important in facilitating interactions between Rtr1, RNAPII, and select transcription factors. Additionally, a putative phosphorylation site was identified on Ser217 of Rtr1 that may also play a role in its recruitment to RNAPII during transcription.
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    A method to isolate the CTD of RNA Polymerase II for proteomics analysis
    (2014-12) Alakhras, Nada S.; Mosley, Amber L.; Goebl, Mark G.; Hurley, Thomas D., 1961-
    In an effort to advance the methodology in analyzing RNAPII protein-protein interaction network and to determine the role of the CTD in controlling RNAPII transcription, we devised a method to specifically isolate the CTD-associated and CTD-less RNAPII to identify the proteins that interact with both the CTD and the globular core of RNAPII using novel purification scheme coupled to quantitative proteomics.
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    Protein function prediction by integrating sequence, structure and binding affinity information
    (2014-02-03) Zhao, Huiying; Zhou, Yaoqi; Liu, Yunlong; Meroueh, Samy; Janga, Sarath Chandra
    Proteins are nano-machines that work inside every living organism. Functional disruption of one or several proteins is the cause for many diseases. However, the functions for most proteins are yet to be annotated because inexpensive sequencing techniques dramatically speed up discovery of new protein sequences (265 million and counting) and experimental examinations of every protein in all its possible functional categories are simply impractical. Thus, it is necessary to develop computational function-prediction tools that complement and guide experimental studies. In this study, we developed a series of predictors for highly accurate prediction of proteins with DNA-binding, RNA-binding and carbohydrate-binding capability. These predictors are a template-based technique that combines sequence and structural information with predicted binding affinity. Both sequence and structure-based approaches were developed. Results indicate the importance of binding affinity prediction for improving sensitivity and precision of function prediction. Application of these methods to the human genome and structure genome targets demonstrated its usefulness in annotating proteins of unknown functions and discovering moon-lighting proteins with DNA,RNA, or carbohydrate binding function. In addition, we also investigated disruption of protein functions by naturally occurring genetic variations due to insertions and deletions (INDELS). We found that protein structures are the most critical features in recognising disease-causing non-frame shifting INDELs. The predictors for function predictions are available at http://sparks-lab.org/spot, and the predictor for classification of non-frame shifting INDELs is available at http://sparks-lab.org/ddig.
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    Role of post-transcriptional regulation in human liver
    (2015-02-11) Chaturvedi, Praneet; Janga, Sarath Chandra
    My thesis comprises of two individual projects which revolve around the importance of post-transcriptional regulation in liver. My first project is studying the integrated miRNA – mRNA network in NAFLD. For fulfillment of the study we conducted a genome-wide study to identify microRNAs (miRs) as well as the miR-mRNA regulatory network associated with hepatic fat and NAFLD. Hepatic fat content (HFC), miR and mRNA expression were assessed in 73 human liver samples. Liver histology of 49 samples was further characterized into normal (n=33) and NAFLD (n=16). Liver miRNome and transcriptome were significantly associated with HFC and utilized to (a) build miR-mRNA association networks in NAFLD and normal livers separately based on the potential miR-mRNA targeting and (b) conduct pathway enrichment analyses. We identified 62 miRs significantly correlated with HFC (p < 0.05 with q < 0.15), with miR-518b and miR-19b being most positively and negatively correlated with HFC, respectively (p < 0.008 for both). Integrated network analysis showed that six miRs (miRs-30b*, 612, 17*, 129-5p, 204 and 20a) controlled ~ 70% of 151 HFC-associated mRNAs (p < 0.001 with q < 0.005). Pathway analyses of these HFC-associated mRNA revealed their key effect (p<0.05) in inflammation pathways and lipid metabolism. Further, significant (p<2.47e-4, Wilcoxon test) reduction in degree of negative associations for HFC-associated miRs with HFC-associated mRNAs was observed in NAFLD as compared to normal livers, strongly suggesting highly dysfunctional miR-mRNA post-transcriptional regulatory network in NAFLD. Our study makes several novel observations which provide clues to better understand the pathogenesis and potential treatment targets of NAFLD. My second project is based on uncovering important players of post-transcriptional regulation (RBPs) and how they are associated with age and gender during healthy liver development. For this study, we performed an association analysis focusing on the expression changes of 1344 RNA Binding proteins (RBPs) as a function of age and gender in human liver. We identify 88 and 45 RBPs to be significantly associated with age and gender respectively. Experimental verification of several of the predicted associations in the mouse model confirmed our findings. Our results suggest that a small fraction of the gender-associated RBPs (~40%) are likely to be up-regulated in males. Altogether, these observations show that several of these RBPs are important developmentally conserved regulators. Further analysis of the protein interaction network of RBPs associated with age and gender based on the centrality measures like degree, betweenness and closeness revealed that several of these RBPs might be prominent players in liver development and impart gender specific alterations in gene expression via the formation of protein complexes. Indeed, both age and gender-associated RBPs in liver were found to show significantly higher clustering coefficients and network centrality measures compared to non-associated RBPs. The compendium of RBPs and this study will help us gain insight into the role of post-transcriptional regulatory molecules in aging and gender specific expression of genes.
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    Transcriptional regulation of ATF4 is critical for controlling the Integrated Stress Response during eIF2 phosphorylation
    (2012-05) Dey, Souvik; Wek, Ronald C.; Edenberg, Howard J.; Gallagher, Patricia; Turchi, John J.
    In response to different environmental stresses, phosphorylation of eIF2 (eIF2P) represses global translation coincident with preferential translation of ATF4. ATF4 is a transcriptional activator of the integrated stress response, a program of gene expression involved in metabolism, nutrient uptake, anti-oxidation, and the activation of additional transcription factors, such as CHOP/GADD153, that can induce apoptosis. Although eIF2P elicits translational control in response to many different stress arrangements, there are selected stresses, such as exposure to UV irradiation, that do not increase ATF4 expression despite robust eIF2P. In this study we addressed the underlying mechanism for variable expression of ATF4 in response to eIF2P during different stress conditions and the biological significance of omission of enhanced ATF4 function. We show that in addition to translational control, ATF4 expression is subject to transcriptional regulation. Stress conditions such as endoplasmic reticulum stress induce both transcription and translation of ATF4, which together enhance expression of ATF4 and its target genes in response to eIF2P. By contrast, UV irradiation represses ATF4 transcription, which diminishes ATF4 mRNA available for translation during eIF2∼P. eIF2P enhances cell survival in response to UV irradiation. However, forced expression of ATF4 and its target gene CHOP leads to increased sensitivity to UV irradiation. In this study, we also show that C/EBPβ is a transcriptional repressor of ATF4 during UV stress. C/EBPβ binds to critical elements in the ATF4 promoter resulting in its transcriptional repression. The LIP isoform of C/EBPβ, but not the LAP version is regulated following UV exposure and directly represses ATF4 transcription. Loss of the LIP isoform results in increased ATF4 mRNA levels in response to UV irradiation, and subsequent recovery of ATF4 translation, leading to enhanced expression of its target genes. Together these results illustrate how eIF2P and translational control, combined with transcription factors regulated by alternative signaling pathways, can direct programs of gene expression that are specifically tailored to each environmental stress.