DNA conformations can be interconverted by relatively mild changes in conditions or can coexist in a single, continuous double helix. The importance of the conformation of the DNA template for in vitro transcription experiments was investigated using a mitochondrial RNA polymerase preparation from Xenopus luevis oocyte mitochondria. The transcribed DNA message, or RNA transcript, is used to produce proteins. DNA is housed within the nucleus of our cells. It controls cellular activity by coding for the production of proteins. This book provides state of the art coverage of the field by covering history of the field, up-to-date topics, clarifications of present day research, and future perspective of what is still to be discovered.