Fig. 3.

Genomic organization of the syncytin-A and -B chromosomal locus. The envelope ORF (open box), the pol-related sequences (dark gray boxes), and murine repetitive elements (light-gray boxes) are indicated. Partial structure of envelope transcripts, as determined experimentally by RT-PCR (with reverse primers in the env ORF) or by an in silico search throughout EST and cDNA databases, are schematized, together with the related splice donor (SD) and splice acceptor (SA) sites positioned on the DNA sequences (with the canonical retroviral envelope SA site in bold).