The double-stranded (ds)
RNA-activated
protein kinase from human cells is a 68,000 Mr
protein (
p68 kinase) induced by
interferon. When autophosphorylated,
p68 kinase catalyzes the phosphorylation of the
protein synthesis
eukaryotic initiation factor-2, thus mediating inhibition of
protein synthesis. The level of
p68 kinase is dramatically reduced in nonionic
detergent NP-40 extracts, obtained from
interferon-treated cells during
infection with encephalomyocarditis virus (EMCV) (A. G. Hovanessian, J. Galabru, E. Meurs, C. Buffet-Janvresse, J. Svab and N. Robert, Virology 159, 126-136, 1987). Here we show that such reduction of
p68 kinase is in fact due to its reduced
NP-40 solubility occurring during EMCV
infection. However,
p68 kinase can be recovered by extraction with an ionic
detergent. Reduced
NP-40 extractibility of
p68 kinase is dependent on the multiplicity of
virus infection and seems to be specific, since other cellular
proteins as well as the 100-kDa
2',5'-oligoadenylate synthetase also induced by
interferon are not modified. Immunofluorescence studies using specific
antibodies demonstrated that
p68 kinase which is distributed evenly in the cytoplasm of HeLa cells becomes concentrated around the nuclei after EMCV
infection. As a consequence of aggregating around the nuclei,
p68 kinase might then resist extraction by
NP-40. The aggregated
kinase is found to be already activated probably due to binding to the replicative form and/or to replicative intermediates of EMCV
RNA. Through this process, the functioning of
p68 kinase might be guaranteed by a localized activation in the replication complexes of EMCV.