Specific cell-induced transformation of Paramecium surface antigens.

Paramecia may induce in other paramecia specific changes in the expression of genes determining surface protein synthesis, probably via cell-to-cell contact. Transformation from one antigenic type to a newly induced one is stimulated by the pretreatment of a cell with 5-fluorouracil. These observations are considered in terms of the regulation of the activity of genes in stable cells and in unstable cells which tend to transform spontaneously.