MxA GTPase blocks reporter gene expression of reconstituted Thogoto virus ribonucleoprotein complexes

Human MxA protein accumulates in the cytoplasm of interferon-treated cells and inhibits the multiplication of several RNA viruses, including Thogota v irus (THOV), a tick-borne orthomyxovirus that transcribes and replicates it s genome in the cell nucleus. The antiviral mechanism of MxA was investigat ed by using two alternative minireplicon systems in which recombinant viral ribonucleoprotein complexes (vRNPs) of THOV were reconstituted from cloned cDNAs, A chloramphenicol acetyltransferase reporter minigenome RNA was exp ressed either by T7 RNA polymerase in the cytoplasm of transfected cells or , alternatively, by RNA polymerase I in the nucleus. The inhibitory effect of MxA was studied in both cellular compartments by coexpressing mild-type MxA or TMxA, an artificial nuclear form of MxA. Our results indicate that b oth MxA proteins recognize the assembled vRNP rather than the newly synthes ized unassembled components. The present findings are consistent with previ ous data which indicated that cytoplasmic MxA prevents transport of vRNPs i nto the nucleus, whereas nuclear MxA directly inhibits the viral polymerase activity in the nucleus.