The nature of thymidine kinase in the human-mouse hybrid cell

In order to characterize the thymidine kinase in human-mouse somatic cell hybrids derived from mouse parental cells lacking thymidine kinase, we have examined the electrophoretic migration on starch gel and the heat sensitivity of this enzyme in human, mouse, and hybrid cells. The enzyme of hybrid cells migrates similarly to that of human fetal liver and human diploid fibroblasts and faster than that of either L or A₉ mouse cells. It is less sensitive to heat than that of the mouse cells. Therefore, the human group E chromosome provides human thymidine kinase for the hybrid cell. The electrophoresis of thymidine kinase makes possible the search for variants.Aided by U.S.P.H.S. Grant No. HD 00486.