Characterization of a regulator of host cell permissiveness to a specific enterovirus

The efficiency of echovirus 6 infection in cultured simian cells is enhanced significantly by a protein isolated from uninfected cultured cells. The enhancer protein was purified and characterized utilizing chromatographic and electrophoretic techniques. The enhancer was eluted from DEAE-cellulose columns with 0.3 M NaCl. Fractionation of these eluates by electrophoresis and isoelectric focusing in polyacrylamide gels indicated that enhancer activity was confined to one or two distinct protein bands. The mobility of the major enhancer band (protein a) in gels of different acrylamide concentrations and under nondenaturing conditions indicated a molecular weight of approximately 68,000. As shown by two-dimensional electrophoresis utilizing sodium dodecyl sulfate in the second dimension, this protein was further dissociated into two subunits, each with a molecular weight of approximately 32,000. The isoelectric point of the enhancer protein was estimated at pH 5.3. This enhancer protein a was detected in extracts from both permissive WISH and semipermissive Vero cells. The presence of the enhancer protein a in Vero cell extracts was demonstrated only in highly concentrated (70x or greater) preparations. There was a direct correlation between concentration of this protein and extent of enhancer activity in cell extracts. These results along with the previous observation that semipermissive cells can be rendered fully permissive by addition of exogenous enhancer suggest that the quantity of enhancer protein regulates host cell permissiveness.