title: The 32-kilobase exp gene cluster of Rhizobium meliloti directing the biosynthesis of galactoglucan: genetic organization and properties of the encoded gene products.
abstract: Proteins directing the biosynthesis of galactoglucan (exopolysaccharide II) in Rhizobium meliloti Rm2011 are encoded by the exp genes. Sequence analysis of a 32-kb DNA fragment of megaplasmid 2 containing the exp gene cluster identified previously (J. Glazebrook and G. C. Walker, Cell 56:661-672, 1989) revealed the presence of 25 open reading frames. Homologies of the deduced exp gene products to proteins of known function suggested that the exp genes encoded four proteins involved in the biosynthesis of dTDP-glucose and dTDP-rhamnose, six glycosyltransferases, an ABC transporter complex homologous to the subfamily of peptide and protein export complexes, and a protein homologous to Rhizobium NodO proteins. In addition, homologies of three Exp proteins to transcriptional regulators, methyltransferases, and periplasmic binding proteins were found. The positions of 26 Tn5 insertions in the exp gene cluster were determined, thus allowing the previously described genetic map to be correlated with the sequence. Operon analysis revealed that the exp gene cluster consists of five complementation groups. In comparison to the wild-type background, all exp complementation groups were transcribed at a substantially elevated level in the regulatory mucR mutant.
authors.affiliation: Lehrstuhl für Genetik, Fakultät fur Biologie, Universität Bielefeld,Germany.
authors.forename: A
authors.initials: A
authors.lastname: Becker
authors.forename: S
authors.initials: S
authors.lastname: Rüberg
authors.forename: H
authors.initials: H
authors.lastname: Küster
authors.forename: A A
authors.initials: AA
authors.lastname: Roxlau
authors.forename: M
authors.initials: M
authors.lastname: Keller
authors.forename: T
authors.initials: T
authors.lastname: Ivashina
authors.forename: H P
authors.initials: HP
authors.lastname: Cheng
authors.forename: G C
authors.initials: GC
authors.lastname: Walker
authors.forename: A
authors.initials: A
authors.lastname: Pühler
mesh_terms: D000595:Amino Acid Sequence; D001426:Bacterial Proteins / Q000235:genetics; D002874:Chromosome Mapping; D004251:DNA Transposable Elements; D005685:Galactans; D015964:Gene Expression Regulation, Bacterial; D005798:Genes, Bacterial; D005816:Genetic Complementation Test; D005936:Glucans; D008969:Molecular Sequence Data; D005810:Multigene Family; D016254:Mutagenesis, Insertional; D011135:Polysaccharides, Bacterial / Q000096:biosynthesis*; D012097:Repressor Proteins; D017422:Sequence Analysis, DNA; D016962:Sinorhizobium meliloti / Q000235:genetics* / Q000378:metabolism; D014157:Transcription Factors; D014158:Transcription, Genetic
chemical_list: D001426:Bacterial Proteins; D004251:DNA Transposable Elements; D005685:Galactans; D005936:Glucans; C093770:MucR protein, Rhizobium meliloti; D011135:Polysaccharides, Bacterial; D012097:Repressor Proteins; D014157:Transcription Factors; C093768:galactoglucan