IDENTIFICATION OF A RETINOIC ACID-INDUCIBLE ENDOGENOUS RETROVIRAL TRANSCRIPT IN THE HUMAN TERATOCARCINOMA-DERIVED CELL-LINE PA-1

Retinoic acid (RA), a developmental morphogen, causes activation of a transcript of an endogenous retrovirus-related element in the human teratocarcinoma-derived cell line PA-1. This provirus is defective, and the provirus-related sequences exist as multicopy elements (more than 20 copies) in human DNA. This is the first human endogenous retroviral mRNA that is known to be transcriptionally activated by RA. The nucleotide sequence of the 3,357 bp of this viral cDNA was determined and shows a strong homology to the type C-related human endogenous retroviral proviruses ERV3 and 4-1. This cDNA contains 'R-U5-DELTA-pol-env-U3-R sequences of the provirus. Adjacent to the putative 5' long terminal repeat of this provirus there is an 18-bp sequence complementary to the 3' end of isoleucine tRNA. We named this RA-responsive virus RRHERV-I.