DNA-mediated transfer of herpes simplex virus TK gene to human TK- cells: properties of the transformed lines.

Human TK- cells carrying the HSV-2 TK gene express a TK activity of viral origin and maintain the TK+ phenotype when grown in HAT medium. Under non-selective or counterselective conditions, however, reversion to a TK- phenotype occurs with a significant frequency characteristic of each transformed line. The TK- phenotype appears to be stable since no instances of TK- to TK+ reversion have been observed.