RNAscope™ 3-plex Positive Control Probe - Mm - RNAscope™ Mouse positive control probe for RNAscope™ Multiplex Fluorescent Assay -Polr2a (C1 channel) and PPIB (C2 channel), UBC (C3 channel) Note: In terms of relative expression levels, UBC is the highest, PPIB is considered a moderate-high, POLR2A is moderate-to low expressor target.