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A Ti or tumour inducing plasmid is a circular plasmid that often, but not always, is a part of the genetic equipment that ''Agrobacterium tumefaciens'' and ''Agrobacterium rhizogenes'' use to transduce its genetic material to plants. The Ti plasmid is lost when ''Agrobacterium'' is grown above 28°C. Such cured bacteria do not induce crown galls, i.e. they become avirulent. pTi and pRi share little sequence homology but are functionally rather similar. The Ti plasmids are classified into different types based on the type of opine produced by their genes. The different opines specified by pTi are octopine, nopaline, succinamopine and leucinopine. The plasmid has 196 genes that code for 195 proteins. There is one structural RNA. The plasmid is 206,479 nucleotides long, the GC content is 56% and 81% of the material is coding genes. There are no pseudogenes. The modification of this plasmid is very important in the creation of transgenic plants. ==Virulence Region== Genes in the virulence region are grouped into the operons ''virABCDEFG'', which code for the enzymes responsible for mediating conjugative transfer of T-DNA to plant cells. * ''virA'' codes for a receptor which reacts to the presence of phenolic compounds such as acetosyringone, syringealdehyde or acetovanillone〔Reconstitution of Acetosyringone-Mediated Agrobacterium tumefaciens Virulence Gene Expression in the Heterologous Host Escherichia coli. Scott M. Lohrke, Hongjiang Yang, and Shouguang Jin, J Bacteriol. 2001 June; 183(12): 3704–3711, 〕 which leak out of damaged plant tissues. * ''virB'' encodes proteins which produce a pore/pilus-like structure.〔 * ''virC'' binds the overdrive sequence.〔 * ''virD1'' and ''virD2'' produce endonucleases which target the direct repeat borders of the T-DNA segment; virD4 is the coupling protein. * ''virE'' binds to T-strand protecting it from nuclease attack, and intercalates with lipids to form channels in the plant membranes through which the T-complex passes,〔 beginning with the right border.〔 * ''virG'' activates vir-gene expression after binding to a consensus sequence,〔 once it has been phosphorylated by ''virA''.〔 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「Ti plasmid」の詳細全文を読む スポンサード リンク
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