[Excision of the plasmid containing the inserted human satellite DNA from Chinese hamster chromosomes after fusion of hamster and human cells].

Fusion of the Chinese hamster stably transformed Tk+ cells containing chromosomally integrated plasmid with a fragment of human satellite III DNA (HS3), with mitomycin C-treated human cells (B-lymphoma, line Raji) results in amplification and excision of heterogeneous plasmid material from hamster chromosomes. Some of these plasmids contain HS3. Functional activity of HS3 in the initiation of DNA replication is shown in transient transfection experiments.

[Genetic transformation of somatic cells. XIII. Limited replication of DNA containing a fragment of human satellite DNA III in mouse cells].

The plasmids containing the variant sequence of human satellite III "rescued" after replication in Chinese hamster cells were transfected into Chinese hamster, mouse and human cells by DEAE-dextran method. Several days after transfection extrachromosomal fractions were isolated, treated with DpnI, transformed into E. coli.

[Isoproterenol stimulation of the repair of single-stranded DNA breaks in Chinese hamster cells induced by gamma irradiation].

The action of the increased intracellular content of adenosine monophosphate (cAMP) in CHO-K1 cells (clones 773 and ADr112eb), treated with isoproterenol, on gamma-induced DNA single-strand breaks repair has been investigated. The hormonal treatment stimulates gamma-induced (180 Gr) DNA single-strand repair during the post-irradiation incubation (45 min) by 75 +/- 16%. The results show the involvement of the cAMP system in radiosensitivity of cultured mammalian cells and in regulation of cellular mechanisms of DNA repair.

[Excision of UV-induced pyrimidine dimers from the DNA of Chinese hamster cells of the CHO line].

Using DNA sedimentation in alkaline sucrose gradients, the excision of pyrimidine dimers from DNA of CHO cells with the help of UV-endonuclease from Micrococcus luteus has been studied. A considerable proportion (approximately 80%) of pyrimidine dimers was shown to be excised within 26 hours, whereas during the initial 17 hours after the UV-fluence (4 J/M2) the excision was slight (approximately 15%).