Figure 4. Quantification of rRNA levels. Total RNA from double mutant yeast was analyzed by microchip electrophoresis to quantitate the levels of 18S and 25S rRNA, which are coordinately processed from the same pre-rRNA transcript. When co-expressed with yeast UTP21 mutations that synthetically interact with the null sti1^- mutation, the K434R variant does not significantly affect 18S rRNA levels.