Specific binding of nuclear proteins to the promoter region of a maize nuclear rRNA gene unit.

The external spacer region of a nuclear rRNA gene unit of maize was analyzed for binding of nuclear proteins and revealed binding to the promoter region and to the 200-base pair repeat elements upstream of the promoter. The promoter binding site was further characterized by DNase I and exonuclease III foot-printing as well as by gel shift and South-Western experiments, revealing the binding of several proteins. Competition experiments indicate that the protein which interacts with the repeat units also binds to the promoter region. A model for the combined action of both binding regions in the regulation of transcription is presented.