A transcript exhibiting homology to endogenous rat retroviral-like elements is regulated by p53

Rat embryo fibroblasts transformed with HPV-16 E7 and the Ha-ras oncogene (ER clones) fall into two distinct groups based on their endogenous p53 status, wild-type or mutant. We have taken advantage of such clones in order to study the p53 target genes by the differential display method of RNA fingerprinting. We have identified a cDNA clone, clone 16, that recognises a large transcript on Northern blots. The clone 16 transcript is overexpressed in ER cell lines that express wild-type p53 compared with ER cell lines that express mutant p53. Similar to the waf1/p21 gene, which is transcriptionally activated in cells treated with ionizing radiation in a p53-dependent manner, the clone 16 transcript was also induced in response to cell irradiation. The sequence of clone 16 exhibits a high homology to two members of RAL retroviral-like elements.