SV40-infected muntjac cells: cell cycle kinetics, cell ploidy and T antigen concentration

Muntjac cells in which the SV40 virus neither readily causes transformation nor replicates were used to study the effect of SV40 infection on cell ploidy and the influence of ploidy on the concentration of T antigen, which is required for the initiation of viral DNA synthesis. Both the DNA content, as measured by the flow microfluorometry of propidium iodide-DNA fluorescence, and the average number of chromosomes per cell indicated that infection with SV40 did not alter the ploidy of the host cell. SV40 infection had no effect on the ploidy distribution of muntjac cells. After immunofluorescence staining with anti-T serum and fluorescein-labeled anti-gamma G, infected and uninfected cultures were compared. In uninfected cells incubated with a 1:20 dilution of anti-T serum no fluorescence could be observed by fluorescence microscopy, but when examined by flow microfluorometry, fluorescence was detected after staining with as little as 1000-fold diluted antiserum. Determination of the amount of T antigen and DNA content in the same cell by simultaneous measurement of fluorescein isothiocyanate-conjugate and propidium iodide fluorescence, indicated that the cellular concentration of T antigen did not vary with the ploidy of the genome or the number of nuclei per cell. These results suggest that gene dosage is not a factor which determines the permissive environment for SV40 replication.