The Xq22.3 HERV-W env locus is transcribed in a sense orientation. The direction of RNA transcripts from the Xq22.3 HERV-W env locus was determined by reverse transcription using strand-specific first strand cDNA synthesis prior to PCR. The localization of the strand-specific primers (depicted by small arrows) relative to the Xq22.3 HERV-W env transcript is shown on top. Total RNA isolated from human PBMC was subjected (+) or not (-) to reverse transcription (RT) using either the sense or antisense primer as strand specific primer in the RT reaction. Subsequent amplification by PCR was performed employing both sense and antisense primers. The expected size of the amplified fragment is 305 bp. H2O, PCR negative control. Human genomic DNA (gDNA) served as positive control.