ACTIVATING-TRANSCRIPTION-FACTOR (ATF) REGULATES HUMAN 7S-L RNA-TRANSCRIPTION BY RNA POLYMERASE-III INVIVO AND INVITRO

The gene-external part of the human 7S L promoter was analyzed by transcription in vitro and in vivo. Compared ot the wild type promoter (-178), a -66 5' deletion mutant revealed full activity in vitro but was efficiently transcribed in vivo. Further deletion to -37 reduced template activity to 50% in vitro and to basal level expression in vivo (below 5%). A DNase I footprint observed around position -50 protected an ATF-like binding site ('TGACGT'). With respect ot 7S L transcription regulation, the functionality of this ATF-like binding site was confirmed in competition experiments and by mutation analysis. Furthermore, S100 extracts of cells pretreated with forskolin in vivo to induce the cAMP system, revealed significantly increased transcription of 7S L RNA in vitro, with no effect on a 7S K RNA gene, lacking such an ATF binding site. Thus, the 7S L RNA gene too is controlled by a regulatory element originally defined in class II promoters and represents another rare example where a specific type of transcription regulation in vivo can be mimicked with cell-free extracts in vitro.