The major promoter element of rRNA transcription in yeast lies 2 kb upstream.

Conventional genetic analysis of the transcription of rDNA in yeast is precluded because the genes are highly reiterated. As an alternative strategy to determine which sequences modulate transcription of pre-rRNA, a series of artificial rRNA genes containing a fragment of DNA from E. coli bacteriophage T7 were introduced into the yeast Saccharomyces cerevisiae. Correct transcription of the artificial genes was observed. Three regions of ribosomal spacer are found to affect transcription of rRNA. Sequences within 210 bp of the 5' terminus of 35S rRNA support low levels of transcription, but at multiple initiation points. Sequences from -210 to -2230 direct correct initiation and increase somewhat the efficiency of transcription. Most striking is that sequences from -2230 to -2420 stimulate transcription 15-fold. The function of this major promoter element is absolutely orientation-dependent but relatively independent of position. Its activity is blocked when an rRNA transcription termination sequence is placed between it and the site of initiation.