A common topology for bacterial and eukaryotic transcription initiation?

DNA supercoiling is a major regulator of transcription in bacteria. Negative supercoiling acts both by promoting the formation of nucleoprotein structures containing wrapped DNA and by altering the twist of DNA. The latter affects the initiation of transcription by RNA polymerase as well as recombination processes. Here, we argue that although bacteria and eukaryotes differ in their mode of packaging DNA supercoils, increases in DNA twist are associated with chromatin folding and transcriptional silencing in both. Conversely, decreases in DNA twist are associated with chromatin unfolding and the acquisition of transcriptional competence. In other words, at the most fundamental level, the principles of genetic regulation are common to all organisms. The apparent differences in the details of regulation probably represent alternative methods of fine-tuning similar underlying processes.