ISOLATION OF FLAT REVERTANTS FROM HUMAN PAPILLOMAVIRUS TYPE-18 E6E7 TRANSFORMED 3Y1 CELLS BY TRANSFECTION WITH A RAT EMBRYO FIBROBLAST CDNAEXPRESSION LIBRARY

A rat embryo fibroblast (REF) cDNA expression library was transfected into 3Y1 cells transformed by human papillomavirus type 18 E6 and E7 g enes and 10 flat revertants were isolated. These revertants expressed the same levels of E6 and E7 mRNA as the parent cells, but had greatly reduced ability to form colonies in soft agar. Suppression of transfo rmation was dominant in cell hybrids generated by fusing each revertan t with the parental transformed cells. Furthermore, loss of transfecte d cDNA was observed in re-transformed cell hybrids derived from one fl at revertant. Overexpression of the cDNA suppresses the colony-forming efficiency of the cells transformed by E6 and E7 genes.