Uptake of minute virus of mice into cultured rodent cells

The uptake of minute virus of mice into cells in tissue culture was examined biochemically and by electron microscopy. Cell-virus complexes were formed at 4 degrees C, and uptake of virus was followed after the cells were shifted to 37 degrees C. The infectious particles appeared to enter cells at 37 degrees C by a two-step process. The first and rapid phase was measured by the resistance of cell-bound virus to elution by EDTA. The bulk of the bound virus particles became refractory to elution with EDTA within 30 min of incubation at 37 degrees C. The infectious particles became resistant to EDTA elution at the same rate. The second, slower phase of the uptake process was measured by the resistance of infectious particles to neutralization by antiserum. This process was complete within 2 h of incubation at 37 degrees C. During this 2-h period, labeled viral DNA became progressively associated with the nuclear fraction of disrupted cells. The uptake of infectious virus could occur during the G1 phase of the cell cycle and was not an S phase-specific event. The uptake process was not the cause of the S phase dependence of minute virus of mice replication. In electron micrographs, virus absorbed to any area of the cell surface appeared to be taken into the cell by pinocytosis.