Sindbis virus infection decreases intracellular pH: alkaline medium inhibits processing of Sindbis virus polyproteins.

Infection of baby hamster kidney cells by Sindbis virus, an alphavirus, resulted in a decrease in the intracellular pH of approximately 0.5 units within the first 1-2 hr after infection as measured either by equilibrium labeling with [14C]benzoic acid or by use of a pH-sensitive fluorescent probe, 2,7-bis-carboxyethyl-5,6-carboxyfluorescein-acetooxymethyl ester. In contrast, intralysosomal pH, as measured using an endocytized pH-sensitive probe, fluorescein isothiocyanate-labeled dextran, was not altered by Sindbis virus infection. Production of Sindbis virus was reduced by more than 90% and post-translational processing of Sindbis virus envelope precursors was inhibited in infected cells incubated in alkaline medium.