Abstract
BAL-31 nuclease was used 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 rRNA synthesis. The major promoter of polymerase I involves the sequence -43 to -27 and the region between nucleotides -18 and +20 contains sequences capable of sustaining a low level of accurate transcription.