Gene expression and intron lengths; transcription rates. The upper panels A and B show expression levels measured by 5'SAGE  and the lower panels C and D show transcription rates measured by a transcription run-on assay . (A) The expression level (5'-SAGE tag count) is depicted versus the intron length. (B) The distributions of the expression levels (5'-SAGE tag counts) are depicted in boxplots for each of the gene sets. (C) The transcription rates (TR) measured two and six hours after glucose-galactose shift are plotted. Measurements of all non-RP genes are depicted as black points. The diagonal line marks the identity. (D) The empirical cumulative distribution functions of TR at six hours of the intron-containing (red) and intronless (blue) RP genes are depicted. For example, a blue point (x,y) represents the fraction y of the intronless RP genes that have smaller TR than x.