RNA Exosome Depletion Reveals Transcription Upstream of Active Human Promoters

Studies have shown that the bulk of eukaryotic genomes is transcribed. Transcriptome maps are frequently updated, but low- abundant transcripts have probably gone unnoticed. To eliminate RNA degradation, we depleted the exonucleolytic RNA exosome from human cells and then subjected the RNA to tiling microarray analysis. This revealed a class of short, polyadenylated and highly unstable RNAs. These promoter upstream transcripts ( PROMPTs) are produced similar to 0.5 to 2.5 kilobases upstream of active transcription start sites. PROMPT transcription occurs in both sense and antisense directions with respect to the downstream gene. In addition, it requires the presence of the gene promoter and is positively correlated with gene activity. We propose that PROMPT transcription is a common characteristic of RNA polymerase II ( RNAPII) transcribed genes with a possible regulatory potential.