Determination of the expression time and the dose--response relationship for mutations at the HGPRT (hypoxanthine-guanine-phosphophoribosyl transferase) locus induced by X-irradiation in human diploid skin fibroblasts.

The length of the expression time for mutants resistant to 8-azaguanine or 6-thioguanine induced by X-rays was determined in human diploid skin fibroblasts. The cells were seeded in the selective medium over a period of 14 days after treatment. Direct expression of at least a part of the mutants was observed at day 0, and an increase of the mutant frequency over the entire cultivation period appeared to be due to spontaneous mutation. The dose-response relationship does not appear to deviate from linearity. The mutation rate per R had a mean value of 2.1 x 10(-7) which is about twice the value of the mutation rate found in rodent cells for the same locus.