Abstract
Isozyme analyses have been carried out to investigate the sites of integration of the herpes simplex type 2 (HSV‐2) thymidine kinase (TK) gene in biochemically transformed human [HeLa(BU25)/HSV‐2–6 Cl 4] cells. Extracts were prepared from He La (BU25)/HSV‐2–6 Cl 4 cells and from human—mouse somatic cell hybrids, which were obtained by fusing the biochemically transformed human cells with TK‐deficient mouse [LM(TK^−^)] cells, and were assayed for 26 isozymes representing markers for 20 human chromosomes. The isozyme analyses were generally consistent with previous karyotype studies, which revealed that the HSV‐2 TK gene was associated with an isochromosome, designated M13, formed from the short arm of human X chromosome in human—mouse hybrid lines HL/2 to HL/7, but with human chromosome 17 containing a trans‐location on the short arm in hybrid line HL/1 and its TK‐positive subclones. The isozyme analyses also indicated that the translocation on the short arm of human chromosome 17 in hybrid line HL/1 was probably derived from human chromosome 21. Hybrid line HL/1 and its TK‐positive subclones expressed a human—mouse heteropolymeric form of superoxide dismutase, a marker for human chromosome 21, but bromodeoxyuridine‐resistant, TK‐negative subclones of HL/1, and hybrid lines HL/3 to HL/6, which did not contain the modified chromosome 17, failed to express the human—mouse heteropolymeric form of superoxide dismutase. The human galactokinase isozyme, which is coded by a gene mapping close to the cytosol TK gene on human chromosome 17, was detected in extracts of TK‐positive HeLa S3, TK‐deficient HeLa(BU25), and biochemically transformed HeLa(BU25)/HSV‐2–6 Cl 4 cells, but not in extracts prepared from human—mouse hybrid line HL/1 and its subclones. These observations suggest that the gene for human galactokinase was either deleted or inactivated in HL/1 and its subclones, perhaps as a result of the translocation to chromosome 17.