Studies on Carcinogenesis by Avian Sarcoma Viruses. III. The Differential Effect of Serum and Polyanions on Multiplication of Unin-

SUMMARY-Infection of chicken embryo cells with avian sarcoma viruses leads to conversion of many properties of the cell. Further.tudies of factors affecting cell multiplication are reported here. Secondary cultures of chicken embryo fibroblasts were prepared in a growth medium containing serum. After incubation overnight, the cultures were exposed to medium from cultures of uninfected or virus-infected cells and various media were then added. The uninfected and the infected cells were allowed to multiply until they reached the stationary phase, at which time their number was determined (saturation density). It was found that the saturation density was proportional to the amount of serum in the growth medium. When serum was limiting, cultures of converted cells multiplied to a saturation density 50 % higher than parallel cultures of uninfected cells. Agar or other polyanions exerted two effects on the saturation density. One was to bind some substance in serum needed for cell multiplication. This substance was used up in cell multiplication and was needed by normal and converted cells. The other was to stimulate multiplication of both uninfected and converted cells. These results lead to the following hypotheses: 1) Multipli-cation of uninfected and converted cells requires a substance, bound by polyanions, which is present in serum. However, the converted cells require less of this substance per cell division than uninfected cells. 2) Cells produce a toxin bound by polyanions. Converted cells produce more of this toxin than uninfected cells.-J Nat Cancer Inst 37: 167-175,1966. SUCCESSFUL INFECTION of a ceU with avian sarcoma virus appears to involve the addition of new genetic information, the provirus (1, 2)