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Three protein fractions that bind to a narrow region of the promoter of the ribosomal RNA gene in Vicia faba.

We previously described the preparation of a protein fraction that bound to the promoter region of the rRNA gene of Vicia faba. We now describe two additional protein fractions that interact with this DNA element. The three protein fractions have similar binding properties with the exception of their binding stabilities. DNase I footprinting experiments revealed that these protein fractions bind to a region that is located about 60 bp upstream from the site of initiation of transcription. From methylation interference experiments and gel-retardation assays with mutated oligonucleotides, it was evident that the protein fractions required the same residues for the formation of stable DNA-protein(s) complexes. However, the three protein fractions were chromatographically distinguishable and the stability of their binding to DNA was different. Although the functions of these fractions are still unknown, the fact that several protein fractions can bind to a narrow region near the site of initiation of transcription is of considerable interest in terms of the mechanism of transcription of the rRNA gene.