Efficient transcription of a protein-coding gene from the RNA polymerase I promoter in transfected cells.

The activity of the mouse ribosomal promoter was examined after fusion to the gene coding for chloramphenicol acetyltransferase (CAT) and transfection into mouse cells. Very little CAT enzyme but high levels of CAT-specific RNA correctly initiated at the ribosomal DNA start site were synthesized. The amount of specific transcripts was neither influenced by long stretches of upstream spacer sequences nor by the insertion of the Moloney murine sarcoma virus enhancer. The deletion mutant pMr delta-39, which has been shown to be fully active in vitro, exhibited a 90% decrease in template activity in vivo. A mutant in which 22 base pairs of ribosomal DNA (between positions -35 and -14) were substituted by foreign DNA sequences proved transcriptionally inactive. The fusion genes were only transcribed in mouse cells, indicating that species-specific transcription factors are involved in ribosomal promoter recognition.