INTERACTIONS WITH SINGLE-STRANDED AND DOUBLE-STRANDED DNA-BINDING FACTORS AND ALTERNATIVE PROMOTER CONFORMATION UPON TRANSCRIPTIONAL ACTIVATION OF THE HTF9-A RANBP1 AND HTF9-C GENES/

The murine Htf9-a/RanBP1 and Htf9-c genes are divergently transcribed from a shared TATA-less promoter. Transcription of both genes is initi ated on complementary DNA strands and is controlled by cell cycle-depe ndent mechanisms, The bidirectional promoter harbors a genomic footpri nt flanking the major transcription start site of both genes, Transien t promoter assays showed that the footprinted element is important for transcription of both genes. Protein-binding experiments and antibody assays indicated that members of the retinoid X receptor family inter act with the double-stranded site, In addition, distinct factors inter act with single DNA strands of the element, Double-stranded binding fa ctors were highly expressed in liver cells, in which neither gene is t ranscribed, while single-stranded binding proteins were abundant in cy cling cells, in which transcription of both genes is efficient, In viv o S1 analysis of the promoter depicted an S1-sensitive organization in cells in which transcription of both genes is active; SI sensitivity was not detected in conditions of transcriptional repression, Thus, th e same element is a target for either retinoid X receptor factors, or for single-stranded binding proteins, and form distinct complexes in d ifferent cellular conditions depending on the DNA conformation in the binding site.