Comparison of pausing with gene activity. Four classes of genes are found when comparing genes with a paused polymerase and transcription activity either by microarray or GRO-seq density in the downstream portions of genes. An example of each class is shown, with tracks shown in the UCSC genome browser as in Fig. 1. The gene names, pausing index, and P value, from top to bottom, respectively, are as follows: TRIO, 1.1, 0.62; FUS, 41, 2.8 × 10−43; IZUMO1, 410, 7.6 × 10−3; and GALP (which has no reads and therefore no pausing index). The number of genes represented in each class is shown to the right.