[Opposite effect of p53 on nucleotide metabolizing enzyme activity in Rat1 cells and their sublines, transformed by N-RAS or v-mos oncogenes].

The effects of exogenous human p53 and its various mutants (Ala-141, His-175, His-194, Trp-248, His-273) on two key enzymes of purine uptake, adenosine deaminase (AD) and hypoxanthine phosphoribosyl transferase (HPRT), has been studied in Rat 1 immortalized fibroblasts and their sublines transformed by N-RAS or v-mos oncogenes. Introduction into Rat1 cells of both wild type (wt) and mutant p53 produced a 2- to 7.5-fold increase in the AD activity, p53 mutants having a stronger effect than p53wt.

[The formation and viability of hybrid cells in a population after irradiation at lethal doses].

With the use of two genetically labeled lines of Djungarian hamster cells and the method of hybrid selection on a HAT-selective medium it was found that in the irradiated mixed culture of the above cell lines, cells were formed that survived in the conditions of total destruction of irradiated parent cells. The chromosome analysis showed that about 45% of the survived cells were hybrids resulting from the radiation-induced fusion of two initial cell lines. These hybrid cells were capable of reproduction.

[Reaction of non-proliferating tumor cells to irradiation].

At early times after irradiation (5 Gy) of HeLa cells at the stationary phase of growth the proliferative pool grows, as compared with the cell culture exposed at the logarithmic phase, and incorporation of 3H-thymidine and 14C-uridine is intensified.

[Reaction of a population of HeLa tumor cells in the stationary stage of growth to irradiation at different rates].

The early stages of a repopulation process of HeLa cells under the action of irradiation 5 Gy dose and an influence of a preliminary 0.1 Gy dose irradiation at that process were investigated. As it was shown the fraction of cells with a great proliferation potential appeared in one day after lethal 5 Gy dose irradiation of the resting HeLa cells.

[Action of ionizing radiation in 3H-thymidine uptake into HeLa cells and DNA synthesis].

DNA synthesis in HeLa cells has been studied radiometrically and autoradiographically within the first 3 hours after gamma-irradiation with 500 rad. It has been shown that changes in the permeability of cell membranes exerted only a slight effect on the 3H-thymidine incorporation in DNA of HeLa cells.