The minus strand and ambisense segmented RNA viruses include multiple important human pathogens and are divided into three families, the Orthomyxoviridae, the Bunyaviridae, and the Arenaviridae. These viruses all initiate viral transcription through the process of ''cap-snatching,'' which involves the acquisition of capped 5 oligonucleotides from cellular mRNA. Hantaviruses are emerging pathogenic viruses of the Bunyaviridae family that replicate in the cytoplasm of infected cells. Cellular mRNAs can be actively translated in polysomes or physically sequestered in cytoplasmic processing bodies (P bodies) where they are degraded or stored for subsequent translation. Here we show that the hantavirus nucleocapsid protein binds with high affinity to the 5 cap of cellular mRNAs, protecting the 5 cap from degradation. We also show that the hantavirus nucleocapsid protein accumulates in P bodies, where it sequesters protected 5 caps. P bodies then serve as a pool of primers during the initiation of viral mRNA synthesis by the viral polymerase. We propose that minus strand segmented viruses replicating in the cytoplasm have co-opted the normal degradation machinery of P bodies for storage of cellular caps. Our data also indicate that modification of the cap-snatching model is warranted to include a role for the nucleocapsid protein in cap acquisition and storage.bunyavirus ͉ minus strand RNA virus ͉ RNA degradation ͉ viral transcription ͉ RNA translation T he paradigm for transcription initiation involving cap-snatching is based on the orthomyxovirus influenza and posits that the heterotrimeric viral RNA-dependent RNA polymerase (RdRp) acquires 5Ј caps through the endonuclease activity of the PB1 subunit of the influenza RdRp (1, 2). This general mechanism of cap-snatching has been assumed for all minus strand segmented RNA viruses including the bunyaviruses and arenaviruses. However, one rather than three genes encode the RdRp of bunyaviruses and arenaviruses, and RdRp-associated endonuclease activity has yet to be established. Moreover, whereas influenza viruses carry out cap-snatching and transcription in the nucleus of infected cells, bunyavirus and arenavirus transcription and genome replication is cytoplasmic (3-8).Cellular mRNA degradation begins with removal of the poly(A) tail. Two alternative pathways that are both dependent on prior deadenylation then further degrade mRNA (9-11). mRNA can undergo 3Ј to 5Ј exonucleolytic decay, catalyzed by cytoplasmic exosomes under the control of peptides of the SKI complex. Alternatively, the 5Ј mRNA cap can be removed by the decapping enzyme DCP2/DCP1, rendering the mRNA susceptible to 5Ј to 3Ј digestion by the exonuclease XRN1. Decapping and XRN1-dependent 5Ј to 3Ј degradation is the predominant pathway for turnover of cellular mRNAs. Moreover, the components of the 5Ј to 3Ј decay machinery, including DCP2/DCP1 and XRN1, as well as a host of other peptides that function in RNA degradation and RNA regulation, are located in discreet cytoplasmic foci called processing bodie...

SUMMARY Pathological hyperphosphorylation and aggregation of tau (pTau) and neuroinflammation, driven by interleukin-1β (IL-1β), are the major hallmarks of tauopathies. Here, we show that pTau primes and activates IL-1β. First, RNA-sequence analysis suggests paired-helical filaments (PHFs) from human tauopathy brain primes nuclear factor κB (NF-κB), chemokine, and IL-1β signaling clusters in human primary microglia. Treating microglia with pTau-containing neuronal media, exosomes, or PHFs causes IL-1β activation, which is NLRP3, ASC, and caspase-1 dependent. Suppression of pTau or ASC reduces tau pathology and inflammasome activation in rTg4510 and hTau mice, respectively. Although the deletion of MyD88 prevents both IL-1β expression and activation in the hTau mouse model of tauopathy, ASC deficiency in myeloid cells reduces pTau-induced IL-1β activation and improves cognitive function in hTau mice. Finally, pTau burden co-exists with elevated IL-1β and ASC in autopsy brains of human tauopathies. Together, our results suggest pTau activates IL-1β via MyD88- and NLRP3-ASC-dependent pathways in myeloid cells, including microglia.

A key genomic characteristic that helps define Hantavirus as a genus of the family Bunyaviridae is the presence of distinctive terminal complementary nucleotides that promote the folding of the viral genomic segments into "panhandle" hairpin structures. The hantavirus nucleocapsid protein (N protein), which is encoded by the smallest of the three negative-sense genomic RNA segments, undergoes in vivo and in vitro trimerization. Trimeric hantavirus N protein specifically recognizes the panhandle structure formed by complementary base sequence of 5 and 3 ends of viral genomic RNA. N protein trimers from the Andes, Puumala, Prospect Hill, Seoul, and Sin Nombre viruses recognize their individual homologous panhandles as well as other hantavirus panhandles with high affinity. In contrast, these hantavirus N proteins bind with markedly reduced affinity to the panhandles from the genera Bunyavirus, Tospovirus, and Phlebovirus or Nairovirus. Interactions between most hantavirus N and heterologous hantavirus viral RNA panhandles are mediated by the nine terminal conserved nucleotides of the panhandle, whereas Sin Nombre virus N requires the first 23 nucleotides for high-affinity binding. Trimeric hantavirus N complexes undergo a prominent conformational change while interacting with panhandles from members of the genus Hantavirus but not while interacting with panhandles from viruses of other genera of the family Bunyaviridae. These data indicate that high-affinity interactions between trimeric N and hantavirus panhandles are conserved within the genus Hantavirus.Hantaviruses are classified as emerging viruses which cause two often fatal diseases that arise by infection of endothelial cells: hemorrhagic fever with renal syndrome and hantavirus cardiopulmonary syndrome (30-33). Each hantavirus is carried by one or a limited number of wild rodent species and transmitted to humans through the aerosol route. The two diseases associated with hantaviruses both cause striking increases in vascular permeability and are elicited by viruses such as Hantaan virus and Sin Nombre virus (SNV), respectively. Hemorrhagic fever with renal syndrome and hantavirus cardiopulmonary syndrome are generally restricted to the Old World and New World, respectively (34). Hantaviruses comprise a genus in the family Bunyaviridae. Members of this virus family have genomes composed of three minus-strand viral RNA (vRNA) segments whose mRNAs encode an RNA-dependent RNA polymerase (RdRp) (L segment), the nucleocapsid protein (N protein; S segment) and G1 and G2 glycoproteins (M segment). The G1 and G2 proteins are posttranslationally processed through the endoplasmic reticulum and Golgi apparatus and ultimately presented on the viral surface. These proteins enable viruses to enter new host cells via their attachment to integrin receptors (7,8). In the virion the three genomic RNA molecules form a complex with N protein and presumably with RdRp.During replication, assembly is initiated with the binding of nucleocapsid protein at a unique encapsidation si...

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Repair of all 12 single-base mismatches in recombination intermediates was investigated in Chinese hamster ovary cells. Extrachromosomal recombination was stimulated by double-strand breaks in regions of shared homology. Recombination was predicted to occur via single-strand annealing, yielding heteroduplex DNA (hDNA) with a single mismatch. Nicks were expected on opposite strands flanking hDNA, equidistant from the mismatch. Unlike studies of covalently closed artificial hDNA substrates, all mismatches were efficiently repaired, consistent with a nick-driven repair process. The average repair efficiency for all mispairs was 92%, with no significant differences among mispairs. There was significant strand-independent repair of G-T → G-C, with a slightly greater bias in a CpG context. Repair of C-A was also biased (toward C-G), but no A-C → G-C bias was found, a possible sequence context effect. No other mismatches showed evidence of biased repair, but among hetero-mismatches, the trend was toward retention of C or G vs. A or T. Repair of both T-T and G-T mismatches was much less efficient in mismatch repair-deficient cells (~25%), and the residual G-T repair was completely biased toward G-C. Our data indicate that single-base mismatches in recombination intermediates are substrates for at least two competing repair systems.