INTERACTIONS BETWEEN THE PROMOTER REGIONS OF NITROGENASE STRUCTURAL GENES (NIFHDK2) AND DNA-BINDING PROTEINS FROM N-2-GROWN AND AMMONIUM-GROWN CELLS OF THE ARCHAEON METHANOSARCINA-BARKERI-227

Transcription initiation in Archaea (archaebacteria) resembles the euc aryotic process, having been shown to involve TATA box-like promoter r egions as well as TATA-binding protein and TFIIB homologs, However, li ttle is known about transcription regulation in archaea. We have previ ously demonstrated that transcripts of nifHDK2 genes, encoding Methano sarcina barkeri nitrogenase, are present in N-2-grown cells but not in ammonium-grown cells, indicating that nif transcription is regulated by the nitrogen source. In this study, we detected proteins in M. bark eri cell extracts that bind specifically to DNA containing the putativ e promoter region of nifTIDK2. No binding was found when the promoter region was deleted from the DNA, A competition assay showed that the m ethyl coenzyme M reductase (mcr) promoter region DNA and the nifH2 pro moter region DNA competed for a common factor(s), There was no binding to the nifH2 promoter region by extracts of ammonium-grown cells, but there was binding by these extracts to promoter regions for mcr genes , which are presumably constitutively expressed. Interestingly, extrac ts of ammonium-grown cells inhibited binding to the nif promoter regio n by extracts of N-2-grown cells, Fractionation of extracts of ammoniu m-grown cells with a heparin-Sepharose column resolved them into a fra ction eluting at 0 M NaCl, which inhibited binding by extracts of N-2- grown cells, and a fraction eluting at 0.5 to 0.75 M: NaCl, which show ed binding to the promoter region, These results are congruent with a model for regulation of nif gene expression in M. barkeri in which a s ubstance present in ammonium-grown cells inhibits DNA binding by a tra nscription-associated protein or proteins.