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Localization of DNA sequences promoting RNA polymerase I activity in Drosophila.

We used BAL-31 nuclease to delete sequences that surround the transcription initiation site of Drosophila ribosomal DNA. A series of deletions was used as templates for in vitro transcription in a Drosophila cell-free system to identify sequences that influence the activity of RNA polymerase I. Sequences that lie upstream of the site of transcription initiation (nucleotide + 1) affect ribosomal RNA synthesis. We show that the major promoter of polymerase I involves the sequence -43 to -27 and that the region between nucleotides -18 and +20 contains sequences capable of sustaining a low level of accurate transcription.