Yvette Škreb

Photorestauration des fragments d'amibes irradiés

Studies were made on the restcration of fragments of amoeba following 1200 ergs/mm/sup 2/ ultraviolet radiation. An excellent restoration of the total quantity of RNA was found. The numbers corresponding to the nucleated fragments illuminated were even superior to those corresponding to the controls. The ratio between illuminated and irradiated fragments was 1.43 and among the anucleated was 1.25. The results confirmed the fact that photorestoration exerts some actual beneficial effects that manifest themselves with different intensity following the cellular constituent considered. It was concluded that the chromophore exists in the cytoplasm of the amoeba since the consequences of the photorestoration manifests itself almost in the same manner in the two types of fragments that are concerned with the evolution of RNA. (P.C.H.)

Influence of gamma-radiation on the incorporation of 14C-adenine and 14C-phenylalanine into whole amoebae and nucleate and anucleate amoeba fragments

Abstract Autoradiographic studies of the incorporation of 14 C-adenine and 14 C-phenylalanine into gamma-irradiated whole amoebae and amoeba fragments have shown that: 1. 1. The synthesis of RNA and proteins in Amoeba proteus is not entirely under nuclear control. 2. 2. The nucleus, though irradiated, can partially repair the damage caused to RNA and protein synthesis by gamma-radiation. 3. 3. The quantity of cytoplasm present during irradiation plays a role in the protection of the nucleus and contributes to its repair.

MODIFICATIONS OF RADIOSENSITIVITY IN NUCLEATE AND ANUCLEATE AMOEBA FRAGMENTS

The objective of this study was to establish: 1 How similar are a real enucleation and the treatment of nucleate Amoeba fragments by actinomycin D or irradiation ? 2 What is the effect of actinomycin D, irradiation or both treatments on the nucleate and anucleate fragments ? 3 Whether radiation damage is reparable. The selected parameters were the metabolism of RNA and proteins followed either by autoradiography after incorporation of specific radioactive precursors or by quantitative determination of these macromolecules. It is concluded: 1 that the three treatments applied separately produce the same effect, and that in both nucleate and anucleate amoeba fragments exposed separately to the effect of radiation or actinomycin D the inhibition level of the synthesis is similar; 2 that after successive application of the two treatments the fragments react differently. Nucleate fragments are more affected by successive application of the two agents than anucleate ones by a single agent. However, the two agents applied to anucleate fragments produce a synergistic effect; 3 that immediately after UV radiation, visible light as well as cooling induce restoration in both kinds of fragments. However, with time, restoration becomes more intense in nucleate fragments, while anucleate fragments die quickly. The results are discussed in connection with cytoplasmic DNA.