PRO-seq experiments in multiple organisms. Also, PRO-seq experiment of Nelfb and Nelfe degron mESC in serum/LIF with or without dTAG-13. Overall design: We used Precision Run-On and Sequencing (PRO-seq) to study transcription in 20 extant organisms that represent very diverse branches on the tree of life, including multiple species near the base of the Metazoa phylogeny and the transition between plants and animals. We also used PRO-seq to study mESCs after degrading NELF-B or NELF-E.