Amplified DNA sequences in Y1 mouse adrenal tumor cells: association with double minutes and localization to a homogeneously staining chromosomal region.

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Abstract
DNA associated with double minutes (dm) of the Y1-DM mouse adrenocortical tumor cell line was cloned in Charon 4A and a preliminary characterization was made of a recombinant clone, .lambda.Y1dm-1, isolated from this dm DNA library. Cloned sequences in .lambda.Y1dm-1 are amplified in the genome of the Y1-DM cells. They are also amplified in the genome of a related Y1 subline (Y1-HSR), which has a homogeneously staining chromosomal region (HSR). The amplified sequences complementary to .lambda.Y1dm-1 are localized to the HSR, as determined by in situ hybridization. A population was found of Y1-DM cells originally containing only dm that later consisted of 2 cell types. Some cells retained dm; others had lost dm but gained a HSR-bearing chromosome morphologically distinct from that in the Y1-HSR cell line. Subclones isolated from this mixed culture have either dm or a HSR, but not both. Southern blotting studies revealed that genomic DNA samples from subclones with a HSR, like subclones with dm, still possess amplified copies of DNA homologous to the recombinant probe. The dm and HSR in these Y1 cells are probably structurally related and the hypothesis that these chromosomal anomalies result from a process of gene amplification is further supported.