The Effect of pH on the Morphology, Electrophoretic Mobility, and Infectivity of the Mouse Mammary Tumor Virus¹ Free

The effect of pH, over the pH range 2 to 12, upon the infectivity and morphology of the mouse mammary tumor virus was determined. The ability of this virus (from RIII milk) to infect and replicate in C57BL mice was essentially constant after being exposed for 30 min to buffers at pH 5 to 11. It was inactive after exposure at pH 2, 4, and 12. Mouse mammary tumor virus was found to be isoelectric at pH 2.5 and migrated as two components at pH values above 3.5. Variation in virion morphology caused by varying the pH of the suspending buffer and the phosphotungstate stain were compared. Particles retained their head-and-tail forms between pH 5 and 8 in the phosphotungstate and between pH 5 and 11 in the buffer. At low pH values the particles were round and penetrated by stain in both procedures. Low-pH buffer degraded the virions severely, whereas low-pH phosphotungstate left both the membrane spikes and the internal structure visible.