MESSENGER-RNA RETROPOSITION IN HUMAN-CELLS - PROCESSED PSEUDOGENE FORMATION

Using a sensitive assay for detection of reverse transcription events, we demonstrate that human HeLa cells can 'retropose', i.e. reverse tr anscribe and integrate, the mRNA of a naive reporter gene, at a low bu t detectable frequency, Furthermore, we show that the retroposed copie s have all the hallmarks of the processed pseudogenes naturally found in the mammalian genome: they lack intron and 5' promoter sequence, th ey have acquired a 3' poly(A) tail, and they are flanked by short repe ats (<15 bp) of target DNA sequence. These results demonstrate that hu man cells possess an endogenous reverse transcription activity, which is not restricted to transcripts of transposable elements, and which i s likely to be involved in the formation, still ongoing, of a large fr action of the eukaryotic genome.