The 5'-upstream Region of the Yeast 25S RRNA Gene Contains a Promoter Element Allowing Expression in Yeast and E. Coli

The 25S rRNA gene of Saccharomyces cerevisiae is preceded by a bona fide TATA sequence which allows the initiation of transcription--presumably by polymerase II--from the same strand as the 25S rRNA gene. When the promoter fragment is cloned in front of a lacZ gene equipped with an initiation codon but lacking a promoter, this element permits formation of beta-galactosidase both in yeast and E. coli. Using RNA from yeast transformed with the fusion plasmid, we mapped by primer elongation a single initiation site 63 bp downstream from the presumed TATA sequence, i.e. about 53 bp 5' of the 25S rRNA gene. A similar signal at about the same position was observed when RNA from untransformed wild-type yeast was used as a template for primer elongation. These results suggest that transcription from this polymerase II promoter-like element occurs in vivo. A regulatory function could not be assigned to this transcript. Its initiation is not significantly influenced by heme or carbon source, although two boxes of high homology with upstream activation sequences (UAS) mediating heme dependent expression of the iso-1-cytochrome c gene (CYC1) precede the promoter at the appropriate distance.