Figure 5.

NMD of GI TER mRNAs occurs in the cytoplasm. (A–C) U2OS PonA cells were transiently transfected with a plasmid producing TER and NORM mRNAs from a bidirectional PonA-regulated promoter that allowed for a calibrated coexpression of both mRNAs within individual cells (Supplemental Fig. S4A,B). mRNA expression was induced using PonA for 20 or 40 min, after which cells were fixed. (A) Maximal projections of cells coexpressing TER and NORM mRNAs after 20 or 40 min of PonA addition. Bar, 5 μm. For each time point (20 min [B] and 40 min [C]), the number of TER mRNAs (B,C; red histograms) and NORM mRNAs (B,C; black histograms) was quantified in the equatorial plane of acquired images in the nucleus, at the DAPI-defined nuclear boundary, and in the cytoplasm. An average number of mRNAs in each compartment for seven (A) and 10 (B) cells ±SEM is shown (see also Supplemental Table S1).