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Vir genes or virulence region of Ti Plasmid

The virulence region of the Ti plasmid mediates the transfer of T DNA and its integration into the plant genome.
Ti plasmid
  • Vir region is organised into 8 operons, vir A to H
  • And has approximately 25 genes.
  • Vir region mediates the transfer of T-DNA to the plant genome.

Vir genes
Vir A
Encodes acetosyringone receptor protein, also activates vir G by phosphprylation leading to constitutive expression of all genes.
Vir B
Encodes membrane protein, involved in conjugal tube formation through which T-DNA is transport.
Vir C
Encodes helicase enzyme; unwinding of T-DNA
Vir D
Topoisomerase activity; vir D2 is an endonucleases
Vir E
Single strand binding protein (SSBP);binds to T-DNA during transfer
Vir F
Activity not known
Vir G
Master controller DNA binding protein; VirA activates vir G by phosphorylation, vir G dimerises and activates constitutive expression of all vir operons
Vir H
Activity not known

All vir genes works in harmony to effect a successful T-DNA transfer into the plant genome.

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