Transcriptional termination occurs at pre-existing signal upstream of ERV. (A) Prematurely terminated transcripts are present at low levels (arrows) in kidneys of mouse strains lacking the polymorphic ERV, indicating that the premature transcriptional polyadenylation signal exists both in strains that have or lack the ERV, and is not templated by the ERV per se. (B, top) Schematic of the Slc15a2 locus showing site of premature transcriptional termination ∼1.5 kb upstream of the intronic ERV polymorphism present in the B6 strain, in intron 7. (Bottom) Sequence trace from 3′-RACE experiment, demonstrating that the 3′ end of the prematurely truncated transcript is polyadenylated ∼1.5 kb upstream of the ERV and contains no ERV-templated sequences per se. (Red arrows) Weak pre-existing polyadenylation signals (i.e., 5′-GATAAA and ATTAAA) are present in the intron, immediately upstream of the added poly(A) tail. GenBank accession numbers JF495121–JF495122.
