The small-t protein of SV40 is required for loss of actin cable networks and plasminogen activator synthesis in transformed rat cells

Of a variety of properties characteristic of SV40 transformed rat embryo fibroblast cells we find that those acquired by minimally transformed cells (the ability to grow clonally and in medium supplemented with low levels of serum) depend only on the large-T protein of SV40 while those properties associated exclusively with fully transformed, tumorigenic cells (growth suspended in methyl cellulose or agar, loss of cytoplasmic actin networks, and synthesis of plasminogen activator) are more likely to occur in cells transformed by viruses which encode the small-t protein as well. In addition one of these properties of the fully transformed cells, PA synthesis, is at least partially independent of large-T activity. Thus the phenotypic difference between the two classes of transformants may be related to the presence or absence of small-t influence within the cell.