Nucleotide sequences of the murine retrovirus Friend SFFVp long terminal repeats: identification of a structure with extensive dyad symmetry 5' to the TATA box.

The two long terminal repeats (LTRs) of the integrated provirus of the polycythemia strain of the Friend spleen focus forming virus have been sequenced. Each of the identical LTRs is 514 nucleotides long and together confer on the provirus the features of a transposable element. They are terminated by perfect 11 base-pair inverted repeats, and the entire provirus is flanked by an apparent duplication of host DNA four nucleotides long. The assumed transcription regulatory sequences (Hogness-Goldberg box, CAAT box, polyadenylation signal) can be identified within the LTRs, as well as a region of an imperfect inverted repeat which extends from approximately 140 to 270 nucleotides 5' from the point of transcription initiation. This sequence may form a hairpin-type structure which might have some function in the promotion of transcription.