A conserved sequence element is present around the transcription initiation site for RNA polymerase A in Saccharomycetoideae

Abstract

To identify DNA elements involved in the initiation of rRNA transcription in yeast we located the start site of the rRNA operon of Kluyveromyces lactis and Hansenula wingei, both members of the Saccharomycetoideae, by S1 nuclease analysis and determined the surrounding nucleotide sequences. Comparison of these sequences with those of Saccharomyces carlsbergensis, S. cerevisiae and S. rosei (all belonging to the same yeast subfamily) reveals an identical sequence at the site of transcription initiation from position +1 to +7 which is part of a larger conserved region extending from position -9 to +23; the conserved heptanucleotide sequence is supposed to constitute an important part of the promoter for yeast RNA polymerase A. The non-transcribed spacers (NTS) upstream of position -9 have diverged strongly with the exception of two short elements around positions -75 and -135. The external transcribed spacer (ETS) downstream of position +23 is largely conserved between K. lactis, S. rosei and S. carlsbergensis except for a divergent region around position +75. On the other hand, the ETS of H. wingei has diverged significantly.