| Abstract: | Two new Djungarian hamster cell lines which are resistant to chloramphenicol (CAP) are described. The clonal DMCAP subline was obtained by incubation of HPRT-deficient DM-15 cells for 6 months in the medium containing 50 micron/ml of CAP. Resistance to CAP is determined in DMCAP cells by the cytoplasm: cytoplasts from these cells could transmit resistance to CAP into sensitive cells, such as L or DMCH-2/1 cells by hybridization. However, after transplantation of DMCAP nuclei into L cytoplasts, the resulting hybrid cells lost resistance to CAP to a great extent. Using the capacity of DMCAP cytoplasts to transfer CAP-resistance, we obtained a line of hybrids (cyt. DMCAP X DMCH-2/1) which was resistant to 8-azaguanine, CAP and colchicine. As in the original DMCH-2/1 cell line, colchicine-resistance in the cybrid line appeared to be associated with gene amplification. Thus, chromosomal analysis showed that the karyotype of the hybrids was identical to that of DMCH-2/1 cells. Both contained marker chromosomes with homogeneously staining regions (HSRs) and, during incubation in the colchicine-free medium, lost resistance to colchicine. The loss of resistance was accompanied by a decrease in the number of cells containing chromosomes with HSRs and an increase in the number with double minutes (DMs). Many cells containing small chromatin bodies in their cytoplasm also appeared. These chromatin bodies may be DMs lost from the nucleus during mitosis. These new sublines with cytoplasmic and nuclear genetic markers may be useful in the further study of cytoplasmic-nuclear interactions, particularly, in the analysis of possible activities of the DNA fragments which appear in the cytoplasm during reversion to colchicine sensitivity. |
