title: One member of a gro-ESL-like chaperonin multigene family in Bradyrhizobium japonicum is co-regulated with symbiotic nitrogen fixation genes.
abstract: This report is concerned with the structural characterization and genetic regulation of new bacterial groES and groEL chaperonin genes, and presents two novelties. The first is the discovery that the nitrogen fixing soybean root nodule bacterium, Bradyrhizobium japonicum, unlike all other prokaryotes investigated so far, possesses a multigene family consisting of five very similar, though not identical, groESL-like genes. The second novelty relates to the finding that these five homologues are expressed to different degrees and, in particular, that one family member (namely groESL3) is induced by a mechanism that does not involve the well-known heat shock response. By contrast, the groESL3 genes are co-regulated together with symbiotic nitrogen fixation genes, in that they are activated by the nitrogen fixation regulatory protein NifA at low oxygen conditions and transcribed from a -24/-12 promoter by the sigma 54 RNA polymerase. Two other members of the groESL gene family are apparently expressed constitutively at different levels, and yet another one is strongly induced by high temperature. As an attractive hypothesis it follows that B. japonicum may modulate its cellular contents of GroES- and GroEL-like chaperonins in response to specific environmental conditions and physiological needs.
authors.affiliation: Mikrobiologisches Institut, Eidgenössische Technische Hochschule, Zürich, Switzerland.
authors.forename: H M
authors.initials: HM
authors.lastname: Fischer
authors.forename: M
authors.initials: M
authors.lastname: Babst
authors.forename: T
authors.initials: T
authors.lastname: Kaspar
authors.forename: G
authors.initials: G
authors.lastname: Acuña
authors.forename: F
authors.initials: F
authors.lastname: Arigoni
authors.forename: H
authors.initials: H
authors.lastname: Hennecke
mesh_terms: D000595:Amino Acid Sequence; D001426:Bacterial Proteins / Q000235:genetics* / Q000378:metabolism; D001483:Base Sequence; D018833:Chaperonins / Q000235:genetics*; D003001:Cloning, Molecular; D004274:DNA, Recombinant; D004926:Escherichia coli / Q000235:genetics; D015964:Gene Expression Regulation, Bacterial; D005798:Genes, Bacterial; D008969:Molecular Sequence Data; D005810:Multigene Family; D009154:Mutation; D009586:Nitrogen Fixation / Q000235:genetics; D009876:Operon; D010641:Phenotype; D010802:Phylogeny; D011401:Promoter Regions, Genetic; D011506:Proteins / Q000235:genetics*; D012230:Rhizobiaceae / Q000235:genetics*; D017422:Sequence Analysis, DNA; D017386:Sequence Homology, Amino Acid; D014157:Transcription Factors / Q000378:metabolism; D014158:Transcription, Genetic
chemical_list: D001426:Bacterial Proteins; D004274:DNA, Recombinant; C097970:GroESL protein, Bacteria; C061338:NifA protein, Bacteria; D011506:Proteins; D014157:Transcription Factors; D018833:Chaperonins