Correspondence

RNA Interference

N Engl J Med 2003; 348:564February 6, 2003

Article

To the Editor:

The article on RNA interference by Kitabwalla and Ruprecht (Oct. 24 issue)1 is most timely in view of the excitement produced by the recent demonstration that small interfering RNAs (siRNAs) have important functions in RNA cleavage involved in host defense against viruses and in the destruction of deleterious messenger RNAs of other kinds. However, I believe the authors err in describing Dicer as an RNA-dependent RNA polymerase limited to plants and drosophila (in the legend to Figure 1 in their article). Dicer was initially described as the endogenous ribonuclease that generates siRNAs from longer double-stranded RNAs2 and appears to be essential to the process of RNA interference in all cases in which siRNA is not supplied exogenously. What may be limited to lower organisms is, rather, the RNA-dependent DNA polymerase capable of spreading the RNA interference phenomenon systemically.3

Peter T. Rowley, M.D.
University of Rochester School of Medicine, Rochester, NY 14642
peter_rowley@urmc.rochester.edu

3 References

1
Kitabwalla M, Ruprecht RM. RNA interference -- a new weapon against HIV and beyond. N Engl J Med 2002;347:1364-1367
Full Text | Web of Science | Medline

2
Bernstein E, Caudy AA, Hammond SM, Hannon GJ. Role for a bidentate ribonuclease in the initiation step of RNA interference. Nature 2001;409:363-366
CrossRef | Web of Science | Medline

3
Sijen T, Fleenor J, Simmer F, et al. On the role of RNA amplification in dsRNA-triggered gene silencing. Cell 2001;107:465-476
CrossRef | Web of Science | Medline

Author/Editor Response

We thank Dr. Rowley for his comment and wish to clarify certain points. The field of RNA interference is moving rapidly. Since we submitted our article, Dicer, an endonuclease that cleaves long double-stranded RNA molecules into fragments of 21 to 23 base pairs,1 has been cloned from complementary DNA libraries of human testis and HeLa cells.2,3 This recombinant human protein was overexpressed in insect cells, purified, and found to cleave double-stranded RNA in cell-free systems into characteristic short fragments.2,3 Thus, Dicer activity has now been found not only in plants and drosophila but in mammalian cells as well, even though enzymes from mammalian organisms appear to differ in their ATP requirements from those of lower organisms.2,3 What seems to be restricted to plants and drosophila is an amplification loop carried out by Dicer in concert with an RNA-dependent RNA polymerase that generates more siRNA molecules for repeated rounds of targeted gene silencing. There is no evidence of involvement of any “RNA-dependent DNA polymerase,” as Dr. Rowley suggests, in the phenomenon of RNA interference.

Moiz Kitabwalla, Ph.D.
Ruth M. Ruprecht, M.D., Ph.D.
Dana–Farber Cancer Institute, Boston, MA 02115
ruth_ruprecht@dfci.harvard.edu

3 References

1
Bernstein E, Caudy AA, Hammond SM, Hannon GJ. Role for a bidentate ribonuclease in the initiation step of RNA interference. Nature 2001;409:363-366
CrossRef | Web of Science | Medline

2
Provost P, Dishart D, Doucet J, Frendewey D, Samuelsson B, Radmark O. Ribonuclease activity and RNA binding of recombinant human Dicer. EMBO J 2002;21:5864-5874
CrossRef | Web of Science | Medline

3
Zhang H, Kolb FA, Brondani V, Billy E, Filipowicz W. Human Dicer preferentially cleaves dsRNAs at their termini without a requirement for ATP. EMBO J 2002;21:5875-5885
CrossRef | Web of Science | Medline

Citing Articles (1)