Retention of herpes simplex virus type II sequences in bglII n-transformed cells after co-transfection with a selectable marker.

Transformation of mammalian cells by total u.v.-inactivated herpes simplex virus II (HSVII) or cloned fragments thereof (BglII n, BglII C) has been complicated both by a low efficiency of oncogenic transformation and the disappearance of viral DNA and/or viral products initially detected in the transformed cell lines. In an attempt to effect a stable integration of BglII n and to elucidate the role of HSVII in oncogenic transformation, we have co-transfected NIH 3T3 cells with pAG60, a plasmid which confers resistance to the G418 antibiotic, and plasmids containing either BglII n in its entirety (pNB2) or one of five subfragments of BglII n. Several isolated clones exhibit a transformed phenotype as expressed by rapid growth in low serum concentrations and colony formation in soft agar. We have obtained a markedly reduced frequency of biochemical transformants when co-transfecting pNB2 in comparison with the numbers obtained when cotransfecting the five subfragments. Furthermore, a greater proportion of subfragment-transfected colonies contain viral DNA, and in higher copy number, than observed in the pAG60/pNB2 clones. We have also found viral DNA to be more stably integrated in the subfragment-transfected clones than in the pNB2-transfected clones.