RNAP II produces capped 18S and 25S ribosomal RNAs resistant to 5-monophosphate dependent processive 5-3 exonuclease in polymerase switched Saccharomyces cerevisiae

We have previously found in the pathogenic yeast Candida albicans, 18S and 25S ribosomal RNA components, containing more than one phosphate on their 5-end, resistant to 5-monophosphate requiring 5[->]3" exonuclease. Several lines of evidence pointed to RNAP II as the enzyme producing them. We now show in Saccharomyces cerevisiae, permanently switched to RNAP II, due to deletion part of RNAP I upstream activator alone or in combination with deletion of one component of RNAP I itself, the production of such 18S and 25S rRNAs. They contain multiple phosphates at their 5-end and an anti-cap specific antibody binds to them indicating capping of these molecules. These molecules are found in RNA isolated from nuclei, therefore are unlikely to be capped in the cytoplasm. This would be unlike recapping of decapped mRNAs which occurs in the cytoplasm. Our data confirm the existence of such molecules and firmly establish RNA II playing a role in their production. The fact that we see these molecules in wild type Saccharomyces cerevisiae indicates that they are not only a result of mutations but are part of the cells physiology. This adds another way RNAP II is involved in ribosome production in addition to their role in the production of ribosome associated proteins.