Transcription regulation by feast/famine regulatory proteins, FFRPs, in archaea and eubacteria.

Feast/famine regulatory proteins (FFRPs) comprise a single group of transcription factors systematically distributed throughout archaea and eubacteria. In the eubacterial domain in Escherichia coli, autotrophic pathways are activated and heterotrophic pathways are repressed by an FFRP, the leucine-responsive regulatory protein (Lrp), in some cases in interaction with other transcription factors. By sensing the concentration of leucine, Lrp changes its association state between hexadecamers and octamers to adapt the autotrophic or heterotrophic mode. The lrp gene is regulated so that the concentration of Lrp decreases in the presence of rich nutrition. In the archaeal domain a large part of the metabolism of Pyrococcus OT3 is regulated by another FFRP, FL11. In the presence of rich nutrition, the metabolism is released from repression by FL11; transcription of fl11 is terminated by FL11 forming octamers in interaction with lysine. When the nutrient is depleted, the metabolism is arrested by a high concentration of FL11; FL11 disassembles to dimers in the absence of lysine, and repression of transcription of fl11 is relaxed. Common characteristics of the master regulations by FL11 and Lrp hint at the prototype regulation once achieved in the common ancestor of all extant organisms. Mechanisms of discrimination by FFRPs between DNA sequences and also between co-regulatory molecules, mostly amino acids, and variations of transcription regulations observed with archaea and eubacteria are reviewed.