Published in Science, vol. 286, no. 5441, pp. 950-952 (October 29, 1999):

Andrew J. Hamilton and David C. Baulcombe

Sainsbury Laboratory, John Innes Centre, Colney Lane,
Norwich NR4 7UH, UK

Posttransciptional gene silencing (PTGS) is a nucleotide sequence-specific defense mechanism that can target both cellular and viral mRNAs. Here, three types of transgene-induced PTGS and one example of virus-induced PTGS were analyzed in plants. In each case, antisense RNA complementary to the targeted mRNA was detected. These RNA molecules were of uniform length, estimated at 25 nucleotides, and their accumulation required either transgene sense transcription or RNA virus replication. Thus, the 25-nucleotide antisense RNA is likely synthesized from an RNA template and may represent the specificity determinant of PTGS.