Structural and functional characterization of the promoter region of the mouse c-Ki-ras gene.

We isolated and characterized the 5' region of the mouse c-Ki-ras gene, including a 5' untranslated exon (exon 0). These studies used genetic material from Y1 mouse adrenocortical tumor cells in which the c-Ki-ras gene is amplified and overexpressed. Our data demonstrate that transcription initiates at multiple sites, predicting size heterogeneity at the 5' ends of the c-Ki-ras mRNAs. Using transient expression assays, we identified a genomic fragment within the 5' region which exhibits bidirectional promoter activity.