Evidence that siRNAs function as guides, not primers, in the Drosophila and human RNAi pathways

Mol Cell. 2002 Sep;10(3):537-48. doi: 10.1016/s1097-2765(02)00651-2.


In Drosophila, two features of small interfering RNA (siRNA) structure--5' phosphates and 3' hydroxyls--are reported to be essential for RNA interference (RNAi). Here, we show that as in Drosophila, a 5' phosphate is required for siRNA function in human HeLa cells. In contrast, we find no evidence in flies or humans for a role in RNAi for the siRNA 3' hydroxyl group. Our in vitro data suggest that in both flies and mammals, each siRNA guides endonucleolytic cleavage of the target RNA at a single site. We conclude that the underlying mechanism of RNAi is conserved between flies and mammals and that RNA-dependent RNA polymerases are not required for RNAi in these organisms.

Publication types

  • Research Support, U.S. Gov't, P.H.S.

MeSH terms

  • Animals
  • Drosophila melanogaster / embryology
  • Drosophila melanogaster / genetics*
  • Endoribonucleases / metabolism
  • Gene Expression Regulation*
  • Genes, Insect
  • HeLa Cells
  • Humans
  • Phosphates / metabolism
  • RNA Interference / physiology*
  • RNA, Double-Stranded / chemistry
  • RNA, Double-Stranded / metabolism
  • RNA, Small Interfering / chemistry
  • RNA, Small Interfering / metabolism*
  • Ribonuclease III


  • Phosphates
  • RNA, Double-Stranded
  • RNA, Small Interfering
  • Endoribonucleases
  • Ribonuclease III