Regulation of transcription occurs through complex interactions of RNA poly
merase and accessory proteins with specific DNA sequences and with each oth
er. The DNA template topology influences the interaction of RNA polymerase
with the promoter and its response to repressors, activators and the intrac
ellular milieu through the formation of altered DNA structures or of nucleo
protein complexes. Recent developments on the role of DNA structures in tra
nscription regulation are discussed.