Explain how transcriptional control by the NrpR protein of the archaeon Methanococcus maripaludis is similar to transcriptional control in bacteria. It is known that 2-oxoglutarate (2OG) is used by cells as an indicator of nitrogen deficiency

Question

Based on what you know about effector molecules in bacterial operons, how would 2OG behave in M. maripaludis (as an inducer, a corepressor, etc.) and what effect would this molecule have on NrpR binding?

Answer 1

NrpR is a transcriptional repressor protein for the two operons, nif and glnA, that are required for nitrogen metabolism. In the presence of nitrogen, the NrpR protein does not bind to the operators and the operons are transcribed; when nitrogen is absent, the operons are repressed because NrpR binds the operator and prevents RNA polymerase from binding. In mutant strains of M. maripaludis that are NrpR−, transcription from these operons is constitutive. This regulation is analogous to the regulation of the lac operon by the lac repressor protein: the presence/absence of lactose influences the binding of the repressor protein to the operator. Repressor binding prevents the recruitment of RNA polymerase, thereby preventing transcription. Bacteria that are lacI− constitutively express -galactosidase and permease.
Since 2OG is present when nitrogen levels are low and since the nif and glnA operons are active in the absence of nitrogen, 2OG will act as an inducer in the M. maripaludis system. Similar to the interaction between allolactose and the lac repressor, 2OG will bind to the NrpR protein to reduce its affinity for the operator and allow binding of RNA polymerase.