Biochemistry, Biophysics, and Structural Biology Commons^™

State-Dependent Mapping Of Glyr-Cholesterol Interactions By Coupling Crosslinking With Mass Spectrometry, Nicholas Ferraro

Electronic Theses and Dissertations

The glycine receptor (GlyR) belongs to a superfamily of pentameric ligand-gated ion channels (pLGICs) that mediate fast neurotransmission. GlyR typically modulates inhibitory transmission by antagonizing membrane depolarization through anion influx. Allosteric interactions between the receptor and its lipid surroundings affect receptor function, and cholesterol is essential for pLGIC activity. Human α1 GlyR was purified from baculovirus infected insect cells and reconstituted in unilamellar vesicles at cholesterol: lipid ratios below and above the cholesterol activity threshold with aliquots of azi-cholesterol. State-dependent crosslinking studies of receptors primarily in its resting (no glycine), desensitized (10mM glycine) and open (F207A/A288G, 30nM ivermectin) states were …

Delivery Of Small Molecule And Rna Using Synthetic Polymeric Micelles And Multifunctional Exosomes For The Treatment Of Type 1 Diabetes, Yang Peng

Theses & Dissertations

Type 1 diabetes is one of the most challenging chronic autoimmune diseases. The destruction and dysfunction of insulin-secreting β cells are the results of inflammatory infiltration and the synergistic effect of multiple immune cells. The aim of this dissertation is to develop novel and reliable therapeutic approaches to advance the treatment of T1D: including chemical modification of a broad-spectrum immunosuppressant, co-application of small molecule based immune intervention and siRNA based β cell preservative therapy, and administration of a PI3K-δ/γ dual inhibitor to specifically target immune cells, utilizing synthetic polymeric micelles or natural produced multi-functional exosomes derived from human bone marrow …

Engineering Hyaluronic Acid For Biomedical Applications, Deep S. Bhattacharya

Theses & Dissertations

This work presents research using the naturally available non- sulfated carbohydrate glycosaminoglycan hyaluronic acid (HA) for the synthesis of different chemical derivatives of HA for evaluation of binding kinetics with CD44 and P- selectin proteins for applications in fluorescence image-guided surgery. Chemical derivatives of HA such as deacetylated HA (deHA), sulfated HA (sHA), and deacetylated and sulfated HA (s-deHA) were synthesized by modulating sulfating and deacetylating reagents to alter binding specificities to CD44. Modified HA derivatives and CD44 biophysical interactions were assessed by fluorescence polarization. In silico techniques were also used to determine binding using molecular docking and MM-PBSA approaches. …

Ecdysoneless, A Novel Regulator Of Ca2+ Homeostasis And Metabolism, Aniruddha Sarkar

Theses & Dissertations

The hallmarks of cancer include sustained proliferation and survival in the face of cellular stresses imposed by the oncogenic drive, as well as metabolic rewiring for tumor growth under adverse nutritional conditions. Adaptive alterations in key biochemical networks that underlie metabolic rewiring represent potential opportunities to develop new therapeutic strategies against cancer.

My thesis focuses on mammalian Ecdysoneless (ECD), a conserved homolog of the fly Ecdysoneless gene product, which engages fundamental cell biological processes of ER stress, Ca²⁺ signaling and metabolism to help sustain the oncogenic drive in tumor cells. Recent studies from our laboratory provide a clear evidence …

Cholesterol Biosynthesis In The Nervous System With An Emphasis On Desmosterolosis, Luke Allen

Theses & Dissertations

Cholesterol biosynthesis is integral to proper neurodevelopment due to the reliance on de novo synthesis of cholesterol in the brain. Disruptions in this process have devastating outcomes for human life characterized by several phenotypic manifestations concomitant with developmental delay. The cholesterol biosynthesis disorder desmosterolosis is an extremely rare disorder with a severe clinical phenotype, however, the models used to study this disease are not well characterized. In addition to genetic disruptions in cholesterol biosynthesis, pharmacological perturbation is an understudied side effect of many commonly prescribed drugs. Here we present a characterization of the sterol profile of the mouse model of …

Brca1 & Ctdp1 Brct Domainomics In The Dna Damage Response, Kimiko L. Krieger

Theses & Dissertations

Genomic instability is one of the enabling characteristics of cancer. DNA damage response pathways are important for genomic integrity and cell cycle progression. Defects in DNA damage repair can often lead to cell cycle arrest, cell death, or tumorigenesis. The activation of the DNA damage response includes tightly regulated signaling cascades that involve kinase phosphorylation and modular domains that scaffold phosphorylated motifs to coordinate recruitment of DNA repair proteins. Modular domains are conserved tertiary structures of a protein that can fold, function, and evolve independently from an intact protein. One of the most common modular domains involved in DNA damage …

Hdac1 Is A Required Cofactor Of Cbfβ-Smmhc And A Therapeutic Target In Inversion 16 Acute Myeloid Leukemia, Lisa E. Richter

Theses & Dissertations

Acute myeloid leukemia (AML) is a neoplastic disease characterized by the uncontrolled proliferation and accumulation of immature myeloid cells. A common mutation in AML is the inversion of chromosome 16 [inv(16)], which generates a fusion between the genes for core binding factor beta (CBFB) and smooth muscle myosin heavy chain (MYH11), forming the oncogene CBFB-MYH11. The expressed protein, CBFβ-SMMHC, forms a heterodimer with the key hematopoietic transcription factor RUNX1. Although CBFβ-SMMHC was previously thought to dominantly repress RUNX1, recent work suggests that CBFβ-SMMHC functions together with RUNX1 to activate transcription of specific target genes.

Targeting the …

The Role Of Reactive Oxygen Species In Regulating Macrophage And Fibroblast Activation Within The Breast Cancer Tumor Microenvironment, Brandon J. Griess

Theses & Dissertations

The tumor microenvironment (TME) is a key determining factor in breast cancer, especially the more aggressive subtype triple negative breast cancer (TNBC). The activated fibroblasts and macrophages within the TME have many tumor promoting functions. Therefore, targeting their activation presents a novel therapeutic approach in TNBC. My work studied the role of reactive oxygen species (ROS) during fibroblast and macrophage activation in breast cancer.

My studies showed that expression of the secreted antioxidant enzyme, EcSOD, is silenced in breast cancer samples, in part, via increased promoter methylation. The re-expression of EcSOD inhibited c-Met activation in the TNBC cell line, MDA-MB231. …

Defining The Role Of Tyrosine Phosphorylation In The Regulation Of Connexin43 In Cardiac Diseases, Li Zheng

Theses & Dissertations

Connexins are integral membrane proteins that oligomerize to form gap junction channels. Ions and small molecules diffuse intercellularly through these channels, allowing individual cellular events to synchronize into the functional response of an entire organ. Gap junction channels composed of Connexin43 (Cx43) mediate electrical coupling and impulse propagation in the normal working myocardium. In the failing heart, Cx43 remodeling (decreased expression, altered phosphorylation state, loss at intercalated discs, and increased presence at lateral membranes) contributes to rhythm disturbances and contractile dysfunction. While there is considerable information regarding key interactions of Cx43 in the regulation of gap junction channels, unfortunately, the …

A Bifunctional Atpase Drives Tad Pilus Extension And Retraction, Courtney K. Ellison, Jingbo Kan, Jennifer L. Chlebek, Katherine R. Hummels, GaёL Panis, Patrick H. Viollier, Nicolas Biais, Ankur B. Dalia, Yves V. Brun

Publications and Research

A widespread class of prokaryotic motors powered by secretion motor adenosine triphosphatases (ATPases) drives the dynamic extension and retraction of extracellular fibers, such as type IV pili (T4P). Among these, the tight adherence (tad) pili are critical for surface sensing and biofilm formation. As for most other motors belonging to this class, how tad pili retract despite lacking a dedicated retraction motor ATPase has remained a mystery. Here, we find that a bifunctional pilus motor ATPase, CpaF, drives both activities through adenosine 5′-triphosphate (ATP) hydrolysis. We show that mutations within CpaF result in a correlated reduction in the rates of …

Alanyl-Trna Synthetase Quality Control Prevents Global Dysregulation Of The Escherichia Coli Proteome, Paul Kelly, Nicholas Backes, Kyle Mohler, Christopher Buser, Arundhati Kavoor, Jesse Rinehart, Gregory Phillips, Michael Ibba

Biology, Chemistry, and Environmental Sciences Faculty Articles and Research

Mechanisms have evolved to prevent errors in replication, transcription, and translation of genetic material, with translational errors occurring most frequently. Errors in protein synthesis can occur at two steps, during tRNA aminoacylation and ribosome decoding. Recent advances in protein mass spectrometry have indicated that previous reports of translational errors have potentially underestimated the frequency of these events, but also that the majority of translational errors occur during ribosomal decoding, suggesting that aminoacylation errors are evolutionarily less tolerated. Despite that interpretation, there is evidence that some aminoacylation errors may be regulated, and thus provide a benefit to the cell, while others …

Single-Nuclei Rna-Seq On Human Retinal Tissue Provides Improved Transcriptome Profiling, Qingnan Liang, Rachayata Dharmat, Leah Owen, Akbar Shakoor, Yumei Li, Sangbae Kim, Albert Vitale, Ivana Kim, Denise Morgan, Shaoheng Liang, Nathaniel Wu, Ken Chen, Margaret M Deangelis, Rui Chen

Faculty, Staff and Students Publications

Single-cell RNA-seq is a powerful tool in decoding the heterogeneity in complex tissues by generating transcriptomic profiles of the individual cell. Here, we report a single-nuclei RNA-seq (snRNA-seq) transcriptomic study on human retinal tissue, which is composed of multiple cell types with distinct functions. Six samples from three healthy donors are profiled and high-quality RNA-seq data is obtained for 5873 single nuclei. All major retinal cell types are observed and marker genes for each cell type are identified. The gene expression of the macular and peripheral retina is compared to each other at cell-type level. Furthermore, our dataset shows an …

Uncovering New Mechanisms Of Cdc34 And Cullin-Ring Activity, Spencer Hill

UNLV Theses, Dissertations, Professional Papers, and Capstones

Ubiquitylation is a cellular regulatory system found in all eukaryotic cells, which has managed to find a role in most pathways imaginable. The system works fundamentally through the ligation of a small protein known as ubiquitin onto a substrate. Depending on the context of the ubiquitin ligation, the substrate can be directed towards a number of cellular fates, the best-studied being degradation of the substrate. While originally thought of as a signal for cellular disposal units to degrade aberrant proteins, we now know that ubiquitin plays a highly nuanced role in cellular epistasis, controlling everything from the cell cycle to …

The Perplexing Paradox Of Clostridioides (Clostridium) Difficile Infection (Cdi) - Analysis Of Anti-Germinants As Part Of Cdi Prophylaxis, Christopher Yip

UNLV Theses, Dissertations, Professional Papers, and Capstones

Clostridioides (Clostridium) difficile infections (CDI) have become the leading cause of nosocomial antibiotic-associated diarrhea worldwide. Under normal circumstances, bacteria found in the gastrointestinal tract provide a barrier against C. difficile colonization. Upon antibiotic therapy, the protective barrier is lost as the microbial community becomes depleted thus providing the opportunity for C. difficile to colonize the human gut. Exposure to taurocholate, a bile acid produced within the mammalian gastrointestinal tract, causes C. difficile spores to begin their transition, a process known as germination, from metabolically dormant structures to toxin-producing cells. As germination is required for the onset of CDI, anti-germination compounds …

Examining Multiple Cellular Pathways At Once Using Multiplex Hextuple Luciferase Assaying, Alejandro Sarrion-Perdigones, Lyra Chang, Yezabel Gonzalez, Tatiana Gallego-Flores, Damian W Young, Koen J T Venken

Faculty, Staff and Students Publications

Sensitive simultaneous assessment of multiple signaling pathways within the same cells requires orthogonal reporters that can assay over large dynamic ranges. Luciferases are such genetically encoded candidates due to their sensitivity, versatility, and cost-effectiveness. We expand luciferase multiplexing in post-lysis endpoint luciferase assays from two to six. Light emissions are distinguished by a combination of distinct substrates and emission spectra deconvolution. All six luciferase reporter units are stitched together into one plasmid facilitating delivery of all reporter units through a process we termed solotransfection, minimizing experimental errors. We engineer a multiplex hextuple luciferase assay to probe pathway fluxes through five …

Residues And Residue Pairs Of Evolutionary Importance Differentially Direct Signaling Bias Of D2 Dopamine Receptors, María E Terrón-Díaz, Sara J Wright, Melina A Agosto, Olivier Lichtarge, Theodore G Wensel

Faculty, Staff and Students Publications

The D2 dopamine receptor and the serotonin 5-hydroxytryptamine 2A receptor (5-HT2A) are closely-related G-protein–coupled receptors (GPCRs) from the class A bioamine subfamily. Despite structural similarity, they respond to distinct ligands through distinct downstream pathways, whose dysregulation is linked to depression, bipolar disorder, addiction, and psychosis. They are important drug targets, and it is important to understand how their bias toward G-protein versus β-arrestin signaling pathways is regulated. Previously, evolution-based computational approaches, difference Evolutionary Trace and Evolutionary Trace–Mutual information (ET-Mip), revealed residues and residue pairs that, when switched in the D2 receptor to the corresponding residues from 5-HT2A, altered ligand potency …

Ultrafast Two-Photon Imaging Of A High-Gain Voltage Indicator In Awake Behaving Mice, Vincent Villette, Mariya Chavarha, Ivan K Dimov, Jonathan Bradley, Lagnajeet Pradhan, Benjamin Mathieu, Stephen W Evans, Simon Chamberland, Dongqing Shi, Renzhi Yang, Benjamin B Kim, Annick Ayon, Abdelali Jalil, François St-Pierre, Mark J Schnitzer, Guoqiang Bi, Katalin Toth, Jun Ding, Stéphane Dieudonné, Michael Z Lin

Faculty, Staff and Students Publications

Optical interrogation of voltage in deep brain locations with cellular resolution would be immensely useful for understanding how neuronal circuits process information. Here, we report ASAP3, a genetically encoded voltage indicator with 51% fluorescence modulation by physiological voltages, submillisecond activation kinetics, and full responsivity under two-photon excitation. We also introduce an ultrafast local volume excitation (ULoVE) method for kilohertz-rate two-photon sampling in vivo with increased stability and sensitivity. Combining a soma-targeted ASAP3 variant and ULoVE, we show single-trial tracking of spikes and subthreshold events for minutes in deep locations, with subcellular resolution and with repeated sampling over days. In the …

Oh Chemistry Of Non-Methane Organic Gases (Nmogs) Emitted From Laboratory And Ambient Biomass Burning Smoke: Evaluating The Influence Of Furans And Oxygenated Aromatics On Ozone And Secondary Nmog Formation, Matthew M. Coggon, Christopher Y. Lim, Abigail R. Koss, Kanako Sekimoto, Bin Yuan, Jessica B. Gilman, David H. Hagan, Vanessa Selimovic, Kyle J. Zarzana, Steven S. Brown, James M Roberts, Markus Müller, Robert Yokelson, Armin Wisthaler, Jordan E. Krechmer, Jose L. Jimenez, Christopher Cappa, Jesse H. Kroll, Joost De Gouw, Carsten Warneke

Chemistry and Biochemistry Faculty Publications

Chamber oxidation experiments conducted at the Fire Sciences Laboratory in 2016 are evaluated to identify important chemical processes contributing to the hydroxy radical (OH) chemistry of biomass burning non-methane organic gases (NMOGs). Based on the decay of primary carbon measured by proton transfer reaction time-of-flight mass spectrometry (PTR-ToF-MS), it is confirmed that furans and oxygenated aromatics are among the NMOGs emitted from western United States fuel types with the highest reactivities towards OH. The oxidation processes and formation of secondary NMOG masses measured by PTR-ToF-MS and iodide-clustering time-of-flight chemical ionization mass spectrometry (I-CIMS) is interpreted using a box model employing …

Characterization Of The Nuclear Pore Complex In Red Alga, Cyanidioschyzon Merolae, Michelle Veronin

Health and Kinesiology Theses

Cyanidioschyzon merolae (C. merolae) is a primitive, unicellular species of red alga that is considered to be one of the simplest self-sustaining eukaryotes. The highly elementary nature of C. merolae makes it an excellent model organism for studying evolution as well as cell function and organelle communication. In our study, we hypothesize that C. merolae contains the minimal assembly of proteins to make up their Nuclear Pore Complexes (NPCs), and hence are the first ancestral NPCs. NPCs are essential for basic nuclear transport in the cell. They are embedded in the double membrane of the nucleus, the …

Total Phenolic And Flavonoid Contents Of Anacyclus Pyrethrum Link Plant Extracts And Their Antioxidant Activity, Hanane Elazzouzi, Nadia Zekri, Touriya Zair, Mohamed Alaoui El Belghiti

Karbala International Journal of Modern Science

In this study, Anacyclus pyrethrm Link (roots) is a medicinal plant from the Asteraceae family, endemic to Morocco and is widely used in traditional medicine; was investigated for their total phenolics, flavonoids contents and antioxidant activities. The quantitative estimation of total flavonoids and phenols by the colorimetric method showed that the extracts were prepared by fractionation of the crude hydromethanolic extract (ethyl acetate and n-butanol). The phenol content of various extracts, estimated by the Folin-Ciocalteu method, was between 1,44 and 12,82 mg EAG / g extract of A. pyrethrum. Moreover, it is clear that ethyl acetate was the …

Structural Basis Of Non-Canonical Transcriptional Regulation By The A-Bound Iron-Sulfur Protein Whib1 In M. Tuberculosis, Tao Wan, Shanren Li, Daisy Guiza Beltran, Andrew Schacht, Lu Zhang, Donald F. Becker, Limei Zhang

Department of Biochemistry: Faculty Publications

WhiB1 is amonomeric iron–sulfur cluster-containing transcription factor in the WhiB-like family that is widely distributed in actinobacteria including the notoriously persistent pathogen Mycobacterium tuberculosis (M. tuberculosis). WhiB1 plays multiple roles in regulating cell growth and responding to nitric oxide stress inM. tuberculosis, but its underlying mechanism is unclear. Here we report a 1.85 A° -resolution crystal structure of the [4Fe–4S] cluster-bound (holo- )WhiB1 in complex with the C-terminal domain of the 70-family primary sigma factor A of M. tuberculosis containing the conserved region 4 (A 4). Region 4 of the 70-family primary sigma factors is commonly used by transcription factors …

Determination Of Optimal Mild Organic Solvents Of Pdnps For Carbon-Carbon Coupling Reactions, Trina Biswas

Honors College Theses

The synthesis of nanoparticles is an increasingly popular field of interest. The application of nanoparticles is especially popular in the field of nanocatalysts. Metal nanoparticles (NPs) are favorable for catalysis because of the large surface area to volume ratio, which allows them to catalyze a variety of reactions using lesser amounts of active material. As the field of nanoparticle research expands, efforts are being made to create more sustainable approaches to the synthesis of these particles. This research sought to translate the benefits of peptide-based synthesis to organic solvents and use less toxic organic solvents for carbon-carbon coupling reactions, like …

Simultaneous Delivery Of Crispr/Cas Complexes And Donor Dna Using Cell-Penetrating Peptide-Adaptors, Maria Mugure Mbugua

Master of Science in Chemical Sciences Theses

Clustered Regularly Interspaced Palindromic Repeats (CRISPR)/CRISPR associated protein (Cas) complexes are becoming the preferred technique for genomic editing because of their precision, efficiency and accuracy. Prokaryotes naturally use CRISPR/Cas complexes to detect and eliminate foreign nucleic acids after infections. Cas proteins form complexes with RNA to cause double-stranded breaks (DSBs) in the invader’s sequence. Researchers are trying to use CRISPR complexes to treat many human diseases caused by these mutations. Research using CRISPR/Cas systems in the treatments of many of the genetic diseases has resulted in misfortunes (such as toxicity to the patient or new diseases) because of the method …

High-Throughput Nano-Scale Characterization Of Membrane Proteins Using Fluorescence-Detection Size-Exclusion Chromatography, Alex J. Vecchio, Robert M. Stroud

Department of Biochemistry: Faculty Publications

Structural biology has revealed predicting heterologous expression levels, homogeneity, and stability of a protein from its primary structure are exceedingly difficult. Membrane proteins, in particular, present numerous challenges that make obtaining milligram quantities of quality samples problematic. For structural and functional investigation of these molecules, however, this is what is required. Fluorescence size-exclusion chromatography (F-SEC), a technique where a protein of biological interest is fused to green fluorescent protein (GFP) and monitored, circumvents many bottlenecks inherent to membrane protein structural biology. In vivo expression yields, as well as in vitro homogeneity and stability, can be rapidly evaluated utilizing nanogram quantities …

Alzheimer's And Amyloid Beta: Amyloidogenicity And Tauopathy Via Dyshomeostatic Interactions Of Amyloid Beta, Jordan Tillinghast

Senior Honors Theses

This paper reviews functions of Amyloid-β (Aβ) in healthy individuals compared to the consequences of aberrant Aβ in Alzheimer’s disease (AD). As extraneuronal Aβ accumulation and plaque formation are characteristics of AD, it is reasonable to infer a pivotal role for Aβ in AD pathogenesis. Establishing progress of the disease as well as the mechanism of neurodegeneration from AD have proven difficult (Selkoe, 1994). This thesis provides evidence suggesting the pathogenesis of AD is due to dysfunctional neuronal processes involving Aβ’s synaptic malfunction, abnormal interaction with tau, and disruption of neuronal homeostasis. Significant evidence demonstrates that AD symptoms are partially …

Differential Analysis Of Individual Centruroides Vittatus Venom

Symposium of Student Scholars

Scorpions are well known, venomous arthropods (Class: Arachnida, Order: Scorpiones). Their venom is composed of neurotoxins, proteases and cytotoxic peptides which plays a major role in toxic components such as inflammatory, antimicrobial and hemolytic activity. Venom is key for the survival of scorpions as it is involved in defense against prey and in feeding on predators. Centruroides vittatus (bark scorpion) is commonly found in North America, with habitat ranges from Nebraska to southern Texas. For this study, scorpions were harvested from Laredo, Texas (27˚57’ N, 99˚43’ W), held in captivity for 4 months and fed a consistent diet of Acheta …

Multidrug Resistance Regulators Mara, Soxs, Rob, And Rama Repress Flagellar Gene Expression And Motility In Salmonella Enterica Serovar Typhimurium, Srinivas Thota, Lon Chubiz

Biology Department Faculty Works

Production of flagella is costly and subject to global multilayered regulation, which is reflected in the hierarchical control of flagellar production in many bacterial species. For Salmonella enterica serovar Typhimurium and its relatives, global regulation of flagellar production primarily occurs through the control of flhDC transcription and mRNA translation. In this study, the roles of the homologous multidrug resistance regulators MarA, SoxS, Rob, and RamA (constituting the mar-sox-rob regulon in S. Typhimurium) in regulating flagellar gene expression were explored. Each of these regulators was found to inhibit flagellar gene expression, production of flagella, and motility. To different degrees, repression via …

Dual Activities Of Plant Cgmp-Dependent Protein Kinase And Its Roles In Gibberellin Signaling And Salt Stress., Qingwen Shen, Xinqiao Zhan, Pei Yang, Jing Li, Jie Chen, Bing Tang, Xuemin Wang, Xuemin Wang, Yueyun Hong

Biology Department Faculty Works

Cyclic GMP (cGMP) is an important regulator in eukaryotes, and cGMP-dependent protein kinase (PKG) plays a key role in perceiving cellular cGMP in diverse physiological processes in animals. However, the molecular identity, property, and function of PKG in plants remain elusive. In this study, we have identified PKG from plants and characterized its role in mediating the gibberellin (GA) response in rice (Oryza sativa). PKGs from plants are structurally unique with an additional type 2C protein phosphatase domain. Rice PKG possesses both protein kinase and phosphatase activities, and cGMP stimulates its kinase activity but inhibits its phosphatase activity. One of …

Comparison Study Of Mold Growth Resistance Of Plastic Based Material Flooring (Pbm Flooring) And Ceramic Tile Flooring, Jyothi Rangineni, Jeremy Tzeng

Publications

Clemson University Department of Biological Sciences and Tile Council of North America Product Performance Testing Laboratory evaluated whether ceramic tile and Plastic Based Material (PBM¹) flooring support mold growth when exposed to fungal spores.

Mold grows in moisture-rich environments and requires only minimal sources of nutrition to support growth. It has long been identified to cause damage to buildings and construction materials and its presence in buildings has been connected to many major health concerns with various studies and reviews published on this matter.²

The method used to evaluate mold growth was ASTM G21-96 (2015).³ This …

Recruitment Of Polycomb-Group Proteins At Giant In Drosophila Embryos, Elnaz Ghotbi Ravandi

Biological Sciences Theses and Dissertations

Polycomb Group (PcG) proteins are evolutionarily conserved epigenetic transcriptional regulators that maintain the transcriptional repression of silenced genes. PcG mediated silencing is divided into two phases: initiation and maintenance. During the initiation phase, PcG proteins initially recognize and bind to their target genes. Once PcG proteins are recruited to their target genes, they can maintain transcriptional repression through an unlimited number of cell cycles. Most studies on PcG proteins have been focused on the maintenance phase of PcG silencing, and the molecular mechanisms by which PcG proteins are initially recruited to their target genes remained unknown. Two models have been …