Transcription Regulators in Archaea: Homologies and Differences with Bacterial Regulators.

The fitness and survival of prokaryotic microorganisms depends on their ability to adequately respond to environmental changes, sudden stress conditions and metabolic shifts. An important mechanism underlying this response is the regulation of gene expression mediated by transcription factors that are responsive to small-molecule ligands or other intracellular signals. Despite constituting a distinct domain of life from bacteria and harboring a eukaryotic-like basal transcription apparatus, it is well established that archaea have similar transcription factors pointing to the existence of shared ancestral proteins and to the occurrence of inter-domain horizontal gene transfer events. However, while global structural features of bacterial and archaeal transcription factors are indeed similar, other characteristics imply that archaeal regulators have undergone independent evolution. Here, we discuss the characteristics of Lrp/AsnC, MarR, ArsR/SmtB and TrmB families of transcription factors, which are the dominant families that constitute the transcription factor repertoire in archaea. We exemplify the evolutionary expansion of these families in archaeal lineages by emphasizing homologies and differences with bacterial counterparts in terms of ligand or signal response, physiological functions and mechanistic principles of regulation. As such, we aim to define future research approaches that enable further characterization of the functions and mechanisms of archaeal transcription factors.