title: Mutation of the miaA gene of Agrobacterium tumefaciens results in reduced vir gene expression.
abstract: vir regulon expression in Agrobacterium tumefaciens involves both chromosome- and Ti-plasmid-encoded gene products. We have isolated and characterized a new chromosomal gene that when mutated results in a 2- to 10-fold reduction in the induced expression of vir genes by acetosyringone. This reduced expression occurs in AB minimal medium (pH 5.5) containing either sucrose or glucose and containing phosphate at high or low concentrations. The locus was cloned and used to complement A. tumefaciens strains harboring Tn5 insertions in the gene. Sequence analysis of this locus revealed an open reading frame with strong homology to the miaA locus of Escherichia coli and the mod5 locus of Saccharomyces cerevisiae. These genes encode tRNA: isopentenyltransferase enzymes responsible for the specific modification of the A-37 residue in UNN codon tRNA species. The function of the homologous gene in A. tumefaciens was proven by genetic complementation of E. coli miaA mutant strains. tRNA undermodification in A. tumefaciens miaA mutant strains may reduce vir gene expression by causing a reduced translation efficiency. A slight reduction in the virulence of these mutant Agrobacterium strains on red potato plants, but not on tobacco, tomato, kalanchoe, or sunflower plants, was observed.
authors.affiliation: Department of Biological Sciences, Purdue University, West Lafayette, Indiana 47907-1392.
authors.forename: J
authors.initials: J
authors.lastname: Gray
authors.forename: J
authors.initials: J
authors.lastname: Wang
authors.forename: S B
authors.initials: SB
authors.lastname: Gelvin
mesh_terms: D000098:Acetophenones / Q000494:pharmacology; D016960:Agrobacterium tumefaciens / Q000187:drug effects / Q000235:genetics*; D019883:Alkyl and Aryl Transferases; D000595:Amino Acid Sequence; D001483:Base Sequence; D015964:Gene Expression Regulation, Bacterial / Q000187:drug effects / Q000235:genetics*; D005816:Genetic Complementation Test; D008969:Molecular Sequence Data; D016254:Mutagenesis, Insertional; D009154:Mutation / Q000235:genetics; D016366:Open Reading Frames / Q000235:genetics; D010944:Plants / Q000382:microbiology; D010957:Plasmids / Q000235:genetics; D011993:Recombinant Fusion Proteins / Q000235:genetics / Q000378:metabolism; D016415:Sequence Alignment; D012689:Sequence Homology, Nucleic Acid; D014166:Transferases / Q000235:genetics*; D001616:beta-Galactosidase / Q000235:genetics / Q000378:metabolism
chemical_list: D000098:Acetophenones; D011993:Recombinant Fusion Proteins; C051667:acetosyringone; D014166:Transferases; D019883:Alkyl and Aryl Transferases; C023197:tRNA isopentenyltransferase; D001616:beta-Galactosidase