Hantaviruses, members of the Bunyaviridae family, are emerging category A pathogens that carry three negative stranded RNA molecules as their genome. Hantavirus nucleocapsid protein (N) is encoded by the smallest S segment genomic RNA (viral RNA). N specifically binds mRNA caps and requires four nucleotides adjacent to the cap for high affinity binding. We show that the N peptide has distinct cap-and RNA-binding sites that independently interact with mRNA cap and viral genomic RNA, respectively. In addition, N can simultaneously bind with both mRNA cap and vRNA. N undergoes distinct conformational changes after binding with either mRNA cap or vRNA or both mRNA cap and vRNA simultaneously. Hantavirus RNA-dependent RNA polymerase (RdRp) uses a capped RNA primer for transcription initiation. The capped RNA primer is generated from host cell mRNA by the cap-snatching mechanism and is supposed to anneal with the 3 terminus of vRNA template during transcription initiation by single G-C base pairing. We show that the capped RNA primer binds at the cap-binding site and induces a conformational change in N. The conformationally altered N with a capped primer loaded at the cap-binding site specifically binds the conserved 3 nine nucleotides of vRNA and assists the bound primer to anneal at the 3 terminus. We suggest that the cap-binding site of N, in conjunction with RdRp, plays a key role during the transcription and replication initiation of vRNA genome.Hantaviruses cause two types of serious human illnesses when transmitted to humans from rodent hosts: hemorrhagic fever with renal syndrome and hantavirus cardiopulmonary syndrome (1, 2). The spherical hantavirus particles harbor three negative sense genomic RNA segments (S, L, and M segments) within a lipid bilayer (3). The mRNAs derived from S, L, and M segments encode viral nucleocapsid protein (N), viral RNA-dependent RNA polymerase (RdRp), 2 and glycoproteins (G1 and G2), respectively. The characteristic feature of the hantaviral genome is the partially complementary sequence at the 5Ј and 3Ј termini of each of the three genome segments that undergo base pairing and form panhandle structures (4 -6). N is a multifunctional protein playing a vital role in multiple processes of virus replication cycle and has been found to undergo trimerization both in vivo and in vitro (7)(8)(9)(10)(11)(12)(13)(14)(15)(16)(17)(18)(19). During encapsidation, the three viral RNA (vRNA) molecules are specifically recognized by N inside the host cell and targeted for packaging. Multiple in vitro studies have shown that N preferentially binds vRNA compared with complementary RNA (cRNA) or nonviral RNA (13, 20 -25). It has been proposed that the specific binding of N with either the panhandle or the sequence at the 5Ј terminus alone selectively facilitates the encapsidation of vRNA to generate three nucleocapsids that are packaged into infectious virions (25, 26). The RNA-binding domain of Hantaan virus N protein has been mapped to the central conserved region corresponding to amino acids f...

Hantavirus glycoprotein precursor (GPC) is posttranslationally cleaved into two glycoproteins, Gn and Gc. Cells transfected with plasmids expressing either GPC or both Gn and Gc revealed that Gn is posttranslationally degraded. Treatment of cells with the autophagy inhibitors 3-methyladenine, LY-294002, or Wortmanin rescued Gn degradation, suggesting that Gn is degraded by the host autophagy machinery. Confocal microscopic imaging showed that Gn is targeted to autophagosomes for degradation by an unknown mechanism. Examination of autophagy markers LC3-I and LC3-II demonstrated that both Gn expression and Sin Nombre hantavirus (SNV) infection induce autophagy in cells. To delineate whether induction of autophagy and clearance of Gn play a role in the virus replication cycle, we downregulated autophagy genes BCLN-1 and ATG7 using small interfering RNA (siRNA) and monitored virus replication over time. These studies revealed that inhibition of host autophagy machinery inhibits Sin Nombre virus replication in cells, suggesting that autophagic clearance of Gn is required for efficient virus replication. Our studies provide mechanistic insights into viral pathogenesis and reveal that SNV exploits the host autophagy machinery to decrease the intrinsic steady-state levels of an important viral component for efficient replication in host cells.

Hantaviruses, members of the Bunyaviridae family, are negative-stranded emerging RNA viruses and category A pathogens that cause serious illness when transmitted to humans through aerosolized excreta of infected rodent hosts. Hantaviruses have evolved a novel translation initiation mechanism, operated by nucleocapsid protein (N), which preferentially facilitates the translation of viral mRNAs. N binds to the ribosomal protein S19 (RPS19), a structural component of the 40 S ribosomal subunit. In addition, N also binds to both the viral mRNA 5 cap and a highly conserved triplet repeat sequence of the viral mRNA 5 UTR. The simultaneous binding of N at both the terminal cap and the 5 UTR favors ribosome loading on viral transcripts during translation initiation. We characterized the binding between N and RPS19 and demonstrate the role of the N-RPS19 interaction in N-mediated translation initiation mechanism. We show that N specifically binds to RPS19 with high affinity and a binding stoichiometry of 1:1. The N-RPS19 interaction is an enthalpy-driven process. RPS19 undergoes a conformational change after binding to N. Using T7 RNA polymerase, we synthesized the hantavirus S segment mRNA, which matches the transcript generated by the viral RNA-dependent RNA polymerase in cells. We show that the N-RPS19 interaction plays a critical role in the translation of this mRNA both in cells and rabbit reticulocyte lysates. Our results demonstrate that the N-mediated translation initiation mechanism, which lures the host translation machinery for the preferential translation of viral transcripts, primarily depends on the N-RPS19 interaction. We suggest that the N-RPS19 interaction is a novel target to shut down the N-mediated translation strategy and hence virus replication in cells.Hantaviruses, members of the Bunyaviridae family, are category A pathogens and causative agents of two emerging diseases: hemorrhagic fever with renal syndrome and hantavirus cardiopulmonary syndrome with mortalities of 15 and 50%, respectively (1, 2). Hantaviruses are transmitted to humans through aerosolized excreta of infected rodent hosts. The spherical hantavirus particles harbor three negative sense genomic RNA segments (S, L, and M) within a lipid bilayer (3). The mRNAs derived from S, L, and M segments encode viral nucleocapsid protein (N), 2 viral RNA-dependent RNA polymerase (RdRp), and glycoprotein precursor, respectively. The glycoprotein precursor is cleaved at a conserved WAASA site, and two glycoproteins, Gn and Gc, are generated (4). The characteristic feature of the hantaviral genome is the partially complementary sequence at the 5Ј and 3Ј termini of each of the three genome segments that undergo base pairing and form panhandle structures (5-7). N is a multifunctional protein playing vital roles in multiple processes of the virus replication cycle and enters the host cell along with viral capsid during infection. N has been found to undergo trimerization both in vivo and in vitro (8 -20). During encapsidation, N specifically recogniz...