Contrasting effects of polycations on plaquing efficiency of encephalomyocarditis virus variants.

Polycation treatment of L cell monolayers affected plaquing efficiency of both the r(+) and r variants of the encephalomyocarditis virus. Plaque formation by r(+) variant was decreased markedly by three structurally different types of synthetic basic polymers, diethylaminoethyl dextran, hexadimethrene (polybrene), and basic polyamino acids. In contrast, these same substances increased substantially the number of plaques formed by the r variant. The effect on the two variants was observed when polycations were applied to the cells before or simultaneously with the introduction of virus. The molar concentration and size of the polymer proved important. Thus, basic polyamino acids of low molecular weight were significantly more inhibitory for the r(+) variant than were those of high molecular weight. On the other hand, plaquing efficiency of the r variant was increased by relatively large polyamino acids, but not by polymers of small size. Basic polyamino acids inhibited r(+) plaque formation to a greater degree at low than at high pH values. However, plaquing efficiency of the r variant in polycation-treated cultures was not affected by changes in pH. Basic polymers appear to bind to cell membranes and affect either attachment or uptake of the viruses. The evidence suggests that the substances influence by different mechanisms the interaction of the r(+) and r variants with cells.