Properties of cells transformed by the middle T-antigen-coding region of polyomavirus.

A series of 10 Fischer rat transformed clonal cell lines were independently obtained in infections with a defective polyomavirus containing a scrambled genome except for an intact middle and small T-antigen-coding region. These cells synthesize middle and small T antigens; no fragment of large T antigen can be detected in any of them. The transformed phenotype of this set of cell lines (designated LT-) has been studied with respect to serum dependence, saturation density, and anchorage independence and compared with the phenotype of a set of six transformants (designated LT+) which synthesize detectable to high levels of shortened or normal-sized large T antigen. Both the LT+ and the LT- groups of polyomavirus transformants display a range of transformed phenotypes. These ranges overlap, and the variations within each group are larger than the variations between the two groups. Thus, the results suggest that, for established Fischer rat fibroblasts, the maintenance of any of the three phenotypes tested and, in particular, of serum independence is not necessarily correlated with the levels of large T antigen or fragments thereof.