Figure 2.

Expression of the two inserts of an IRES construct is correlated at median expression levels but not at high expression levels. A. HEK293 cells transfected with tdTomato.pIRES2.EGFP express both green (EGFP) and red (tdTomato) fluorescence signals. Scale bar: 100 μm (for all panels). B. The expression level of the EGFP marker 3’ to the IRES site has an increased coefficient of variance (62.7%) compared to the tdTomato gene 5’ to the IRES site (40.6%). Boxes represent quartiles (25^th-75^th percentile), the line is the median, and whiskers for the 5^th-95^th percentile with the indicated dots as values outside the 5^th-95^th percentile. C. Pearson’s correlation test for matched pairs of EGFP and tdTomato fluorescence signals (P<0.001, R²=0.236, n=362 cells). High relative fluorescence/expression of the product of one of the two genes flanking the IRES site is predictive of low relative fluorescence/expression of the product of the other gene.