Fragile X Mental Retardation Protein (FMRP) is a regulatory RNA binding protein that plays a central role in the development of several human disorders including Fragile X Syndrome (FXS) and autism. FMRP uses an arginine-glycine-rich (RGG) motif for specific interactions with guanine (G)-quadruplexes, mRNA elements implicated in the disease-associated regulation of specific mRNAs. Here we report the 2.8-Å crystal structure of the complex between the human FMRP RGG peptide bound to the in vitro selected G-rich RNA. In this model system, the RNA adopts an intramolecular K + -stabilized G-quadruplex structure composed of three G-quartets and a mixed tetrad connected to an RNA duplex. The RGG peptide specifically binds to the duplex-quadruplex junction, the mixed tetrad, and the duplex region of the RNA through shape complementarity, cation-π interactions, and multiple hydrogen bonds. Many of these interactions critically depend on a type I β-turn, a secondary structure element whose formation was not previously recognized in the RGG motif of FMRP. RNA mutagenesis and footprinting experiments indicate that interactions of the peptide with the duplex-quadruplex junction and the duplex of RNA are equally important for affinity and specificity of the RGG-RNA complex formation. These results suggest that specific binding of cellular RNAs by FMRP may involve hydrogen bonding with RNA duplexes and that RNA duplex recognition can be a characteristic RNA binding feature for RGG motifs in other proteins.R NA-binding proteins (RBPs) control all aspects of RNA metabolism and are fundamental to core cellular processes. ∼14% of identified human RBPs are implicated in a broad spectrum of human pathologies, including neurodegenerative and muscular diseases, metabolic disorders, and cancers (1, 2). Fragile X Mental Retardation Protein (FMRP) is among the most important RBPs because of its central role in several human diseases (3). Loss of FMRP function due to CGG triplet repeat expansion-associated transcriptional silencing or missense mutations in the protein (4, 5) lead to fragile X syndrome (FXS), the most common cause of inherited intellectual disability. Mutations in FMRP are also the leading monogenic cause of autism (6, 7). Intermediate length repeat expansions in the FMR1 gene are linked to fragile X-associated tremor ataxia syndrome (8) and fragile X-associated primary ovarian insufficiency (9).FMRP contains four canonical nucleic acid-binding motifs, three KH domains and one arginine-glycine-rich (RGG) box, which mediate interactions with RNAs in mRNA transport, storage, stability, and regulation of translation (Fig. 1A) (3, 10). Each KH domain has been reported to have a mutation either causing FXS or found in patients with intellectual disability (4, 5, 11). In neurons, FMRP associates with a subset of mRNAs and represses their translation both in the cell body and near synapses (12). Loss of repression of these mRNAs is associated with alterations in synaptic plasticity and dendritic spine dynamics thought to underlie...

Highlights d Cryo-EM structures suggest a mechanism of H2BK120Ubmediated stimulation of Dot1L d Dot1L interacts with histone H4, the acidic patch, DNA, and ubiquitin d Dot1L/ubiquitin interactions stabilize the conformation of the enzyme on the nucleosome d H2BK120Ub enables Dot1L to catalyze higher methylation states of H3K79

Emergent resistance to all clinical antibiotics calls for the next generation of therapeutics. Here we report an effective antimicrobial strategy targeting the bacterial hydrogen sulfide (H2S)–mediated defense system. We identified cystathionine γ-lyase (CSE) as the primary generator of H2S in two major human pathogens, Staphylococcus aureus and Pseudomonas aeruginosa, and discovered small molecules that inhibit bacterial CSE. These inhibitors potentiate bactericidal antibiotics against both pathogens in vitro and in mouse models of infection. CSE inhibitors also suppress bacterial tolerance, disrupting biofilm formation and substantially reducing the number of persister bacteria that survive antibiotic treatment. Our results establish bacterial H2S as a multifunctional defense factor and CSE as a drug target for versatile antibiotic enhancers.

SUMMARY RNA modifications that once escaped detection are now thought to be pivotal for governing RNA lifetimes in both prokaryotes and eukaryotes. For example, converting the 5′-terminal triphosphate of bacterial transcripts to a monophosphate triggers 5′-end-dependent degradation by RNase E. However, the existence of diphosphorylated RNA in bacteria has never been reported, and no biological role for such a modification has ever been proposed. By using a novel assay, we show here for representative Escherichia coli mRNAs that ~35–50% of each transcript is diphosphorylated. The remainder is primarily monophosphorylated, with surprisingly little triphosphorylated RNA evident. Furthermore, diphosphorylated RNA is the preferred substrate of the RNA pyrophosphohydrolase RppH, whose biological function was previously assumed to be pyrophosphate removal from triphosphorylated transcripts. We conclude that triphosphate-to-monophosphate conversion to induce 5′-end-dependent RNA degradation is a two-step process in E. coli involving γ-phosphate removal by an unidentified enzyme to enable subsequent β-phosphate removal by RppH.