HA titers and Vp1 expression levels of JCV Vp1 cysteine point mutants in mammalian cells.

<p>(A) Schematic diagram of cysteine point mutant Vp1s. Each of the six cysteine residues in the 354-amino-acid JCV Vp1 is marked with a “C” for the WT Vp1 (WT), and the cysteine residue mutated into alanine is designated as “A” for each point mutant Vp1. (B) HA titers of extracts from Vp1-expressing cells. HA titers were determined from the last dilution showing hemagglutination for two-fold serially diluted extracts prepared from HeLa cells transfected with the expression plasmids for WT or individual point mutant Vp1s. The corresponding dilutions of extract from JCV-infected cells served as a positive control, whereas those of PBS or of HeLa extract from transfection with the empty plasmid (Mock) were used as negative controls. (C) Levels of Vp1 expression. Quantitation of the mutant Vp1s and actin in HeLa cells transfected with the Vp1 expression plasmids or with an empty vector (Mock) were analyzed by SDS-PAGE and immunoblotting for Vp1 (Vp1) and for actin (act).