ras oncogene activates the intracisternal A particle long terminal repeat promoter through a c-AMP response element

To understand the mechanism responsible for the high expression of Intracisternal A Particles (IAP) in murine cells transformed by the Kirsten Mouse Sarcoma Virus (Ki-MSV), we have investigated the effect of p21ras on IAP transcription. By transient cotransfections of IAP LTR-CAT plasmids with v-Ki-ras and c-Ki-ras expression vectors, we have found that p21v-Ki-ras, and the p21c-Ki-ras to a lesser extent, stimulate the promoter activity of the 5' IAP LTR. We constructed several plasmids containing the CAT gene under control of IAP LTRs deleted in different regions. CAT assays demonstrate that the ras responsive sequence is a 16 bp oligonucleotide containing an effective c-AMP Response Element (CRE) TGACGTCA, which is located in the U3 region, 20 bp upstream of the CAAT box.