We have isolated cDNA clones complementary to a c-Ki-ras cellular oncogene that is amplified in Y1 mouse adrenal tumor cells, with the amplified sequences located on double-minute chromatin bodies (DMs) and homogeneously staining chromosomal regions (HSRs). Characterization of the cDNAs included the isolation of corresponding genomic clones, Northern blot analysis of RNA, and DNA sequence analysis. Our studies demonstrate that the c-Ki-ras gene amplified in the Y1 cells is homologous to the human c-Ki-ras2 gene. We have also obtained evidence that, in addition to c-Ki-ras, at least one other transcription unit has been amplified in the mouse adrenal tumor cells. Moreover, by Southern blot analysis of Chinese hamster-mouse somatic cell hybrids, we have determined that the amplified DNA sequences associated with DMs and HSRs, including the c-Ki-ras gene, are present in normal mouse cells on chromosome 6.
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