Transcriptional regulation at a distance in bacteria

Transcriptional enhancers are cis-acting DNA elements that are binding site s for regulatory proteins and function at large distances from promoter ele ments to stimulate transcription. Once thought to be. unique to eukaryotes, enhancer-like elements have been discovered in a wide variety of bacteria. The regulatory proteins that bind to these bacterial enhancers must contac t RNA. polymerase to activate transcription, in principle, interactions bet ween bacterial enhancer-binding proteins and RNA polymerase san occur by ei ther DNA looping or tracking of the enhancer-binding protein along the DNA. Paradigms for each of these methods are round in bacterial systems. Activa tors of sigma (54)-RNA polymerase holoenzyme contact polymerase by DNA loop ing, while bacteriophage T4 gp45 functions as a sliding clamp that tracks a long DNA until it engages RNA polymerase. Significant advances have been ma de over the last few veers towards understanding the mechanisms by which ba cterial enhancer-binding proteins activate transcription, but important asp ects of these mechanisms are still poorly defined.