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VirA Senses, VirG Transcribes, VirD Cleaves, VirE Coats, VirB Channels
Picture This (Mental Hook): Nature's genetic engineer Agrobacterium attacks a wounded plant: VirA sniffs wounded plant phenolic perfume (Acetosyringone). VirA activates VirG the general. VirG orders VirD scissors to snip T-DNA at 25 bp borders. VirE coats the single-strand T-DNA like a winter scarf. And VirB builds the channel tunnel into plant cells!
📊 Visual Diagram & Mental Flow:
Wounded Plant releases Acetosyringone (Phenolic signal)
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[VirA] (Transmembrane sensor kinase phosphorylates)
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[VirG] (Cytoplasmic response regulator activates all vir promoters)
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┌────────────────────────┼────────────────────────┐
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[VirD1/D2] Endonuclease [VirE2] Single-strand [VirB1-11] Type IV
Cuts Left & Right DNA binding protein Secretion Channel across
Borders of T-DNA protects T-strand bacterial membrane🔍 The Decoded Sequence:
VirA / VirG
Two-Component Regulatory
VirA receptor detects acetosyringone; VirG transcriptional activator
VirD2
Pilot Protein
Nicks 25-bp direct border repeats and covalently attaches to 5' end of T-DNA
T-DNA
Transferred DNA
Contains genes for auxin (iaaM/iaaH), cytokinin (ipt), and opines (crown gall tumor!)
Examiner Trap / Never Forget: In disarmed Ti cloning vectors used in modern plant biotechnology, the tumor-inducing auxin/cytokinin oncogenes are DELETED, but the 25-bp Left and Right Borders (LB/RB) and vir helper genes MUST be retained!
