Characterization of the virB operon of an Agrobacterium tumefaciens Ti plasmid: nucleotide sequence and protein analysis.
The virulence regulon of the Agrobacterium tumefaciens TiC58 plasmid is composed of six operons, virA, virB, virG, virC, virD and virE, which direct the transfer of T-DNA into plant cells. The 9.5 kbp virB operon is the largest of these operons and its entire nucleotide sequence was determined and found to contain eleven open reading frames (ORFs). Gene fusions of each VirB ORF to T7 phi 10 were made and overexpressed in Escherichia coli to confirm that they encode proteins of predicted size. Hydrophobic analysis of these peptide sequences revealed nine proteins that contain hydrophobic spanning regions including signal-peptide-like sequences. These data suggest that the majority of VirB proteins may associate with bacterial cell membranes, while the two additional proteins possess a potential ATP-binding site. Strong homologies in amino acid sequences were observed between nopaline- and octopine-type plasmids. Specific differences in amino acid sequence encoded by VirB ORFs of nopaline and octopine Ti plasmid and a functional role of the gene products are discussed.
Shirasu
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K
Department of Plant Pathology, University of California, Davis 95616.
Morel
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P
Kado
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CI
D000255:Adenosine Triphosphate / Q000378:metabolism; D000595:Amino Acid Sequence; D001120:Arginine / Q000031:analogs & derivatives / Q000235:genetics; D001426:Bacterial Proteins / Q000235:genetics*; D001483:Base Sequence; D001665:Binding Sites; D015964:Gene Expression Regulation, Bacterial; D008969:Molecular Sequence Data; D009876:Operon; D010957:Plasmids; D012231:Rhizobium / Q000235:genetics*; D012689:Sequence Homology, Nucleic Acid; D037521:Virulence Factors
D001426:Bacterial Proteins; D037521:Virulence Factors; C008666:nopaline; C005394:octopine; D000255:Adenosine Triphosphate; D001120:Arginine