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Structure of a Neurospora RNA polymerase I promoter defined by transcription in vitro with homologous extracts.

A Neurospora in vitro transcription system has been developed which specifically and efficiently initiates transcription of a cloned Neurospora crassa ribosomal RNA gene by RNA polymerase I. The initiation site of transcription (both in vitro and in vivo) appears to be located about 850 bp from the 5' end of mature 17S rRNA. However, the primary rRNA transcripts are normally cleaved very rapidly at a site 120-125 nt from the 5' end in vitro and in vivo. The nucleotide sequence surrounding the initiation site has been determined. The region from -16 to +9 exhibits partial homology to the corresponding sequences from a wide variety of organisms including yeast, but the most striking similarity is to the initiation region from Dictyostelium discoideum which displays 73% homology to the Neurospora sequence from -23 to +47. The Neurospora sequences from -96 to +97 have been shown to be sufficient for transcription. This region contains two sequences displaying 8/9 bp matches to elements of the 5S rDNA promoter.