Sequence alignment of IAP LTRs. “IR” indicates 4-bp inverted repeat. Note that Prnp^a –IAP LTRs contained several putative binding sites found in other IAP LTRs: (1) a consensus binding site (GCCGCCCCCA) for the transcription factor SP1; (2) a binding site (TGTTCT) for the glucocorticoid responsive element (GRE) of mouse mammary tumor virus (MMTV) (Scheidereit et al. 1983); (3) (CORE), Transcription enhancer sequence (AGTGGTAAA) that shares homology with the SV40 enhancer motif [TGTGGTA(T/A)] (Weiher et al. 1983); and (4) a consensus binding site (GTGACGTCA) for the transcription factor AP1 (Lee et al. 1987). (CAT and TATA) Promoter boxes that together may determine the transcriptional initiation site. (POLY A) indicates polyadenylation site.