Lavie L, Maldener E, Brouha B, Meese EU, Mayer J.

Genome Res. 2004 Nov;14(11):2253-60 doi:10.1101/gr.2745804

The human L1 promoter: variable transcription initiation sites and a major impact of upstream flanking sequence on promoter activity.

The presence of an extra G in pseudogenes suggests that many reverse-transcriptases can reverse transcribe the cap.