Structure and expression of amplified cKi-ras gene sequences in Y1 mouse adrenal tumor cells.

A recombinant library of double minute chromosomal DNA, enriched in specific sequences that are amplified in Y1 mouse adrenal tumor cells, was used as a source of material to explore the structure and expression of amplified cKi-ras genes in these cells. From DNA sequence analysis of these cloned fragments, we found no evidence for the presence of point mutations previously demonstrated to be associated with activation of the transforming potential of ras genes. A comparison of the mouse gene with that of the homologous human cKi-ras2 gene reveals 94% nucleotide sequence homology within the coding regions and 97% homology for the predicted amino acid composition. Like the human gene, the mouse cKi-ras gene contains alternative 3' coding exons. Blot hybridization analyses of RNA revealed a preferential utilization of the more 3' of the two fourth coding exons in the generation of Y1 cKi-ras transcripts.