Post Transcriptional Gene Silencing in Plants (PTGS) - Eurasnet.info

Viral strategies for suppression and evasion of RNA-silencinga | Direct interference with silencing-effectormolecules is illustrated by the tombusviral P19protein. The head-to-tail organization of thetombusviral P19 homodimers (blue and green)allows binding to small interfering RNA (siRNA)duplexes (yellow). Two sets of tryptophanresidues (yellow) bind to the last set of base pairson either end of the siRNA, leading to effectivemeasurement of the duplex length, such that P19selects siRNAs of 21nt for binding. Thesequestered siRNA is prevented from enteringthe RNA induced silencing complex (RISC) andis therefore inactivated.b | Recruitment of endogenous negativeregulators of RNA silencing is illustrated by thepotyviral helper component proteinase (HcPro).HcPro interacts with the calmodulin-like proteinrgsCaM (regulator of gene silencing CaM) toinactivate the RNA-silencing pathway throughan unknown mechanism at an intermediate stepthat involves both RISC and Dicer.