Dependence of expression level and 5'UTR length. (A) Expression levels (5'-SAGE tag counts) are depicted in relation to the lengths of the 5'UTRs using different symbols for the two RP gene sets. (B) The length distributions of the 5'UTRs of intron-containing (x) and intronless (y) RP genes are compared in a Quantile-Quantile plot. For example, the 0.9-quantile of x is the value (5'UTR length) k such that 90% of all x-values are smaller than k. The quantiles of the two distributions are plotted against each other to identify systematic deviations. The diagonal line marks equality.