Schematic rendition of a dynamic transcription factory in which the loops of 13 genomic loci for the ten nuclear-encoded COX subunit genes and genes for Tfam, Tfb1m, and Tfb2m are cotranscribed, with the aid of RNA polymerase II, NRF-1, NRF-2, and possibly other transcription factors and coactivators. (Reproduced with permission from Dhar et al 2009a).