Mechanistic characterization of the 5′-triphosphate-dependent activation of PKR: Lack of 5′-end nucleobase specificity, evidence for a distinct triphosphate binding site, and a critical role for the dsRBD

The protein kinase PKR is activated by RNA to phosphorylate eIF-2α, inhibiting translation initiation. Long dsRNA activates PKR via interactions with the dsRNA-binding domain (dsRBD). Weakly structured RNA also activates PKR and does so in a 5′-triphosphate (ppp)–dependent fashion, however relatively little is known about this pathway. We used a mutant T7 RNA polymerase to incorporate all four triphosphate-containing nucleotides into the first position of a largely single-stranded RNA and found absence of selectivity, in that all four transcripts activate PKR. Recognition of 5′-triphosphate, but not the nucleobase at the 5′-most position, makes this RNA-mediated innate immune response sensitive to a broad array of viruses. PKR was neither activated in the presence of γ-GTP nor recognized NTPs other than ATP in activation competition and ITC binding assays. This indicates that the binding site for ATP is selective, which contrasts with the site for the 5′ end of ppp-ssRNA. Activation experiments reveal that short dsRNAs compete with 5′-triphosphate RNAs and heparin for activation, and likewise gel-shift assays reveal that activating 5′-triphosphate RNAs and heparin compete with short dsRNAs for binding to PKR's dsRBD. The dsRBD thus plays a critical role in the activation of PKR by ppp-ssRNA and even heparin. At the same time, cross-linking experiments indicate that ppp-ssRNA interacts with PKR outside of the dsRBD as well. Overall, 5′-triphosphate-containing, weakly structured RNAs activate PKR via interactions with both the dsRBD and a distinct triphosphate binding site that lacks 5′-nucleobase specificity, allowing the innate immune response to provide broad-spectrum protection from pathogens

The influence of viral RNA secondary structure on interactions with innate host cell defences

RNA viruses infecting vertebrates differ fundamentally in their ability to establish persistent infections with markedly different patterns of transmission, disease mechanisms and evolutionary relationships with their hosts. Although interactions with host innate and adaptive responses are complex and persistence mechanisms likely multi-factorial, we previously observed associations between bioinformatically predicted RNA secondary formation in genomes of positive-stranded RNA viruses with their in vivo fitness and persistence. To analyse this interactions functionally, we transfected fibroblasts with non-replicating, non-translated RNA transcripts from RNA viral genomes with differing degrees of genome-scale ordered RNA structure (GORS). Single-stranded RNA transcripts induced interferon-β mediated though RIG-I and PKR activation, the latter associated with rapid induction of antiviral stress granules. A striking inverse correlation was observed between induction of both cellular responses with transcript RNA structure formation that was independent of both nucleotide composition and sequence length. The consistent inability of cells to recognize RNA transcripts possessing GORS extended to downstream differences from unstructured transcripts in expression of TNF-α, other interferon-stimulated genes and induction of apoptosis. This functional association provides novel insights into interactions between virus and host early after infection and provides evidence for a novel mechanism for evading intrinsic and innate immune responses

Termination of pre-mRNA splicing requires that the ATPase and RNA unwindase Prp43p acts on the catalytic snRNA U6

The termination of pre-mRNA splicing functions to discard suboptimal substrates, thereby enhancing fidelity, and to release excised introns in a manner coupled to spliceosome disassembly, thereby allowing recycling. The mechanism of termination, including the RNA target of the DEAH-box ATPase Prp43p, remains ambiguous. We discovered a critical role for nucleotides at the 3′ end of the catalytic U6 small nuclear RNA in splicing termination. Although conserved sequence at the 3′ end is not required, 2′ hydroxyls are, paralleling requirements for Prp43p biochemical activities. Although the 3′ end of U6 is not required for recruiting Prp43p to the spliceosome, the 3′ end cross-links directly to Prp43p in an RNA-dependent manner. Our data indicate a mechanism of splicing termination in which Prp43p translocates along U6 from the 3′ end to disassemble the spliceosome and thereby release suboptimal substrates or excised introns. This mechanism reveals that the spliceosome becomes primed for termination at the same stage it becomes activated for catalysis, implying a requirement for stringent control of spliceosome activity within the cell.</jats:p

Termination of pre-mRNA splicing requires that the ATPase and RNA unwindase Prp43 acts on the catalytic snRNA U6

AbstractThe termination of pre-mRNA splicing functions to discard suboptimal substrates, thereby enhancing fidelity, and to release excised introns in a manner coupled to spliceosome disassembly, thereby allowing recycling. The mechanism of termination, including the RNA target of the DEAH-box ATPase Prp43, remains ambiguous. We discovered a critical role for nucleotides at the 3’-end of the catalytic U6 small nuclear RNA in splicing termination. Though conserved sequence at the 3’-end is not required, 2’ hydroxyls are, paralleling requirements for Prp43 biochemical activities. While the 3’-end of U6 is not required for recruiting Prp43 to the spliceosome, the 3’ end crosslinks directly to Prp43 in an RNA-dependent manner. Our data indicate a mechanism of splicing termination in which Prp43 translocates along U6 from the 3’ end to disassemble the spliceosome and thereby release suboptimal substrates or excised introns. This mechanism reveals that the spliceosome becomes primed for termination at the same stage it becomes activated for catalysis, implying a requirement for stringent control of spliceosome activity within the cell.</jats:p

Brief Report: Impact of COVID-19 on Individuals with ASD and Their Caregivers: A Perspective from the SPARK Cohort

The impact of the 2019 coronavirus pandemic (COVID-19) in the United States is unprecedented, with unknown implications for the autism community. We surveyed 3502 parents/caregivers of individuals with an autism spectrum disorder (ASD) enrolled in Simons Powering Autism Research for Knowledge (SPARK) and found that most individuals with ASD experienced significant, ongoing disruptions to therapies. While some services were adapted to telehealth format, most participants were not receiving such services at follow-up, and those who were reported minimal benefit. Children under age five had the most severely disrupted services and lowest reported benefit of telehealth adaptation. Caregivers also reported worsening ASD symptoms and moderate family distress. Strategies to support the ASD community should be immediately developed and implemented

Brief Report: Impact of COVID-19 on Individuals with ASD and Their Caregivers: A Perspective from the SPARK Cohort

The impact of the 2019 coronavirus pandemic (COVID-19) in the United States is unprecedented, with unknown implications for the autism community. We surveyed 3502 parents/caregivers of individuals with an autism spectrum disorder (ASD) enrolled in Simons Powering Autism Research for Knowledge (SPARK) and found that most individuals with ASD experienced significant, ongoing disruptions to therapies. While some services were adapted to telehealth format, most participants were not receiving such services at follow-up, and those who were reported minimal benefit. Children under age five had the most severely disrupted services and lowest reported benefit of telehealth adaptation. Caregivers also reported worsening ASD symptoms and moderate family distress. Strategies to support the ASD community should be immediately developed and implemented