virG, an Agrobacterium tumefaciens transcriptional activator, initiates translation at a UUG codon and is a sequence-specific DNA-binding protein

J Bacteriol. 1990 Mar;172(3):1241-9. doi: 10.1128/jb.172.3.1241-1249.1990.

Abstract

The Agrobacterium tumefaciens Ti plasmid virG locus, in conjunction with virA and acetosyringone, activates transcription of the virulence (vir) genes. Insertional and deoxyoligonucleotide-directed mutagenesis studies showed that both octopine and nopaline Ti plasmid virG genes initiate translation at a UUG codon. VirG protein initiated at this UUG codon was found to be 241 amino acid residues in length and had an apparent molecular mass of 27.1 kilodaltons. A Salmonella typhimurium trp-virG transcriptional fusion was constructed to overproduce VirG. Agrobacterium cells containing this gene fusion showed a large increase in virG activity in the presence of virA and acetosyringone. Since the trp promoter is not under virA-virG control, this result indicates that modification of VirG is necessary for its full activity. VirG overproduced in Escherichia coli was purified from inclusion bodies. It was found to be a DNA-binding protein that preferentially bound DNA fragments containing the 5' nontranscribed regions of the virA, -B, -C, -D, and -G operons. Significant specific binding to the 5' nontranscribed region sequences of virE was not detected. DNase I footprinting of the upstream regions of virC-virD and virG showed that VirG binds to sequences around the vir box region.

Publication types

  • Research Support, Non-U.S. Gov't
  • Research Support, U.S. Gov't, P.H.S.

MeSH terms

  • Bacterial Proteins / metabolism*
  • Base Sequence
  • Codon / genetics*
  • DNA-Binding Proteins / metabolism*
  • Genes, Bacterial*
  • Molecular Sequence Data
  • Mutation
  • Oligonucleotide Probes
  • Plasmids
  • Protein Biosynthesis*
  • RNA, Messenger / genetics*
  • Rhizobium / genetics*
  • Rhizobium / metabolism
  • Rhizobium / pathogenicity
  • Transcription Factors*
  • Transcriptional Activation*
  • Virulence

Substances

  • Bacterial Proteins
  • Codon
  • DNA-Binding Proteins
  • Oligonucleotide Probes
  • RNA, Messenger
  • Transcription Factors
  • virG protein, Shigella flexneri