The influenza A virus RNA polymerase is a heterotrimer that transcribes and replicates the viral genome in the cell nucleus. Newly synthesized RNA polymerase subunits must therefore be imported into the nucleus during an infection. While various models have been proposed for this process, the consensus is that the polymerase basic protein PB1 and polymerase acidic protein PA subunits form a dimer in the cytoplasm and are transported into the nucleus by the betaimportin Ran-binding protein 5 (RanBP5), with the PB2 subunit imported separately to complete the trimeric complex. In this study, we characterized the interaction of PB1 with RanBP5 further and assessed its importance for viral growth. In particular, we found that the N-terminal region of PB1 mediates its binding to RanBP5 and that basic residues in a nuclear localization signal are required for RanBP5 binding. Mutating these basic residues to alanines does not prevent PB1 forming a dimer with PA, but does reduce RanBP5 binding. RanBP5-binding mutations reduce, though do not entirely prevent, the nuclear accumulation of PB1. Furthermore, mutations affecting RanBP5 binding are incompatible with or severely attenuate viral growth, providing further support for a key role for RanBP5 in the influenza A virus life cycle. INTRODUCTIONInfluenza A virus is the prototypic orthomyxovirus and a serious pathogen of humans and animals. The viral genome consists of eight segments of negative-sense, ssRNA, which are encapsidated as viral ribonucleoprotein complexes (vRNPs) by multiple copies of nucleoprotein (NP) and the trimeric RNA-dependent RNA polymerase (RdRP; consisting of the polymerase basic proteins PB1 and PB2, and the polymerase acidic protein PA) (Palese & Shaw, 2007). Unusually among RNA viruses, orthomyxoviruses replicate their genomes in the nucleus. Consequently, newly synthesized viral proteins must be imported into the nucleus to allow the assembly and export of new vRNPs, as well as to regulate host processes in the infected cell. Of the proteins expressed by influenza A virus, nuclear import is observed for the three polymerase proteins and NP, as well as matrix (M1) protein, non-structural (NS1) protein, nuclear export protein (NEP) and PB1-F2 (Chen et al., 2001;Smith et al., 1987). Nuclear import of structures larger than 20-30 kDa is selective and energy dependent, requiring binding of nuclear import factors (NIFs) through nuclear localization signals (NLSs) on import substrates (Görlich & Kutay, 1999). A number of influenza A virus proteins have been shown to contain NLSs and to bind NIFs Naito et al., 2007; Resa-Infante et al., 2008;Tarendeau et al., 2007). PB1 and PA, despite both having signals that can promote nuclear import when individually expressed (Akkina et al., 1987;Nath & Nayak, 1990;Nieto et al., 1994), do not accumulate efficiently in the nucleus unless expressed together, a requirement that appears to be particularly marked for PB1 (Fodor & Smith, 2004;Huet et al., 2010;Nieto et al., 1992). Although all possible pairwise interact...
Objective To identify and characterise non-specific immunological effects after routine childhood vaccines against BCG, measles, diphtheria, pertussis, and tetanus.Design Systematic review of randomised controlled trials, cohort studies, and case-control studies.Data sources Embase, PubMed, Cochrane library, and Trip searched between 1947 and January 2014. Publications submitted by a panel of experts in the specialty were also included.Eligibility criteria for selecting studies All human studies reporting non-specific immunological effects after vaccination with standard childhood immunisations. Studies using recombinant vaccines, no vaccine at all, or reporting only vaccine specific outcomes were excluded. The primary aim was to systematically identify, assemble, and review all available studies and data on the possible non-specific or heterologous immunological effects of BCG; measles; mumps, measles, and rubella (MMR); diphtheria; tetanus; and pertussis vaccines.Results The initial search yielded 11 168 references; 77 manuscripts met the inclusion criteria for data analysis. In most included studies (48%) BCG was the vaccine intervention. The final time point of outcome measurement was primarily performed (70%) between one and 12 months after vaccination. There was a high risk of bias in the included studies, with no single study rated low risk across all assessment criteria. A total of 143 different immunological variables were reported, which, in conjunction with differences in measurement units and summary statistics, created a high number of combinations thus precluding any meta-analysis. Studies that compared BCG vaccinated with unvaccinated groups showed a trend towards increased IFN-γ production in vitro in the vaccinated groups. Increases were also observed for IFN-γ measured after BCG vaccination in response to in vitro stimulation with microbial antigens from Candida albicans, tetanus toxoid, Staphylococcus aureas, lipopolysaccharide, and hepatitis B. Cohort studies of measles vaccination showed an increase in lymphoproliferation to microbial antigens from tetanus toxoid and C albicans. Increases in immunogenicity to heterologous antigens were noted after diphtheria-tetanus (herpes simplex virus and polio antibody titres) and diphtheria-tetanus-pertussis (pneumococcus serotype 14 and polio neutralising responses) vaccination.Conclusions The papers reporting non-specific immunological effects had heterogeneous study designs and could not be conventionally meta-analysed, providing a low level of evidence quality. Some studies, such as BCG vaccine studies examining in vitro IFN-γ responses and measles vaccine studies examining lymphoproliferation to microbial antigen stimulation, showed a consistent direction of effect suggestive of non-specific immunological effects. The quality of the evidence, however, does not provide confidence in the nature, magnitude, or timing of non-specific immunological effects after vaccination with BCG, diphtheria, pertussis, tetanus, or measles containing vaccines nor the ...
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