(3/3) We also include new simulations showing cluster visibility over background is mediated by # of engaged polymerases at a locus. Our data + sim. show that RNAPII clusters do not require higher-order assembly mechanisms and reflect local accumulations of transcriptionally engaged polymerases.

(2/3) Previously, we had only looked at one gene (hunchback). Here, we extend our study to 3 additional genes (eve, snail, and sog), sister chromatids, and include multiple controls (non-transcribing loci and control spots) to more definitively claim single-cluster association with individual genes.