%0 Journal Article %A Bacchetti, S. %A Graham, F. L. %T Characterization of Human TK− Cell Lines Transformed to a TK+ Phenotype by Herpes Simplex Virus Type 2 DNA %D 1979 %J Journal of General Virology, %V 42 %N 1 %P 149-157 %@ 1465-2099 %R https://doi.org/10.1099/0022-1317-42-1-149 %I Microbiology Society, %X SUMMARY Human TK− cells carrying the HSV-2 TK gene as a result of transformation with virus DNA express a TK activity of virus origin and maintain the TK+ phenotype when grown in HAT medium. Under non-selective conditions, however, reversion to a TK− phenotype occurs with a significant frequency characteristic of each transformed line. Once reversion has occurred the TK− phenotype appears to be stable, since only very rare instances of TK− to TK+ reversion have been observed. TK− revertants were susceptible to re-transformation by virus DNA, but no reactivation of a silent virus TK gene could be obtained by superinfecting them with a TK− virus mutant. The data presented are consistent with the hypothesis that acquisition of the TK− phenotype is brought about by loss of the virus sequences coding for TK. %U https://www.microbiologyresearch.org/content/journal/jgv/10.1099/0022-1317-42-1-149