[The kinetics of polykaryon formation in a HeLa cell culture after irradiation at doses of 5 and 10 Gy]. / Kinetika obrazovaniia polikarionov v kul'ture kletok HeLa posle oblucheniia v dozakh 5 i 10 Gr.

Monolayer culture of HeLa tumor cells irradiated at 5 Gy and 10 Gy doses was followed up in kinetics for 14 days. It was shown that starting with day 3 the cell monolayer is modified in such a way that some cells occur in 2- to 8-cell accumulations. The rate of formation of such groups and the number of cells in them were dose-related. The labeling index in these formations was several times higher than that in the irradiated population on the whole. The analysis of the grade of DNA synthesis synchronization in these accumulations showed that complete cell fusion and polykaryon formation after irradiation at the dose of 10 Gy occurred on day 4 whereas after 5 Gy, only on day 7. In both cases the status of complete fusion was 3 days in duration.

[A decrease in the efficiency of radiation damage repair in HeLa tumor cells with their preliminary irradiation at low radiation doses (0.1 Gr)]. / Snizhenie éffektivnosti reparatsii radiatsionnykh povrezhdenii v opukholevykh kletkakh HeLa pri predvaritel'nom obluchenii v malykh dozakh radiatsii (0,1 Gr).

In experiments with tumor HeLa cells, a study was made of the survival rate of both the whole population and individual clonogenic cells after irradiation within different regimes at a cumulative dose of 4 Gy. The results obtained prompt a conclusion that the preirradiation with a dose of 0.1 Gy decreases the efficiency of repair of radiation-induced damages to cells.

[Effect of low doses of ionizing radiation on the kinetics of growth of a population of HeLa tumor cells]. / Vliianie malykh doz ioniziruiushchego izlucheniia na kinetiku rosta populiatsii opukholevykh kletok HeLa.

While studying the effect of 0.1 Gy radiation on the growth of HeLa cells the authors have revealed an increase in the share of cells with the increased proliferative activity that cannot transfer to the resting state.

[Changes in the self ultraviolet fluorescence of HeLa cells undergoing ionizing irradiation]. / Izmenenie sobstvennoi ul'trafioletovoi fluorestsentsii kletok HeLa, obluchennykh ioniziruiushchim izlucheniem.

A study was made of the influence of irradiation on the ultra-violet fluorescence respond of the resting HeLa cells being in the stationary growth phase. No change in the cell ultra-violet fluorescence (UVF) intensity was seen immediately after irradiation (1.5 hours). The time dynamics observation of fluorescence intensity changes after irradiation demonstrated the highest values of UVF on the 3rd day--at the start proliferating point. At doses of 10 and 500 rad the action of irradiation on HeLa cells has an opposite UVF respond, compared with the control. The effect of the 500 rad dose irradiation increases the cell UVF intensity on the 3rd recultivating day, but the 10 rad dose irradiation makes it lower compared to the control level. Radiometric analysis makes it clear that HeLa cell UVF changes are not related to the change of protein synthesis with the precursors of 3H-tryptophan.

[The nucleases of oxytetracycline producing actinomycetes]. / Nukleazy aktinomitsetov--produtsentov oksitetratsiklina

The activity of exocellular nucleases, especially RNase, differs among cultures producing oxytetracycline, and belonging or similar to Actinomyces rimosus, and cultures which are not related to this species. The activity of RNase therefore may be regarded as an additional taxonomic characteristic within the species Act. rimosus. Formation of various enzymes involved in synthesis of nucleic acids was studied with the strain of Act. re end of fermentation, the content of the antibiotic and the activity of exocellular and endocellular RNases and DNases in the cultural broth were maximal. The cultural broth therefore may be used as a source of both oxytetracycline and nucleases.