Different RNA polymerase states show distinct exon biases. Pie charts representing the percentage of exons in each category at RNA polymerase enrichment locations. These include exons from enrichment locations that include more than one exon. PolIIa is strongly biased towards transcription initiation locations. Most of the internal exons are second exons overlapping with first exons. The phosphorylation-independent antibody recognizes PolII at both transcription initiation and termination locations with a slight bias towards termination locations.