Animal Communication: Hidden Complexity

dots the authors were also able to estimate the number of elongating Pol II complexes along the length of the MS2/lacZ transgene. These calculations suggest that there are approximately 30 elongating Pol II complexes distributed along the length of the transgene at maximal induction. This corresponds to a density of one Pol II complex every 150 basepairs, or one Pol II released from the promoter every six seconds. This is quite a high rate of RNA synthesis, given that the theoretical limit is approximately one Pol II complex every 70–80 basepairs due to the large size of the Pol II footprint. These studies are the harbingers of things to come: the visualization of time. We are getting the first glimpses into the dynamic activation of gene expression during development. There is no going back, and there is little doubt that these studies are ushering in a new era for the elucidation of temporal control, comparable to the insights gained into the spatial regulation of gene expression provided by the fixed in situ hybridization methods first introduced around 30 years ago [14–16]. At long last, the dynamic developing embryo is ready for its close-up.