Official websites use. Share sensitive information only on official, secure websites. RNA silencing phenomena were first discovered in plants, yet only the RNA interference pathway in animals has been subject to biochemical analysis. Here, we extend biochemical analysis to plant RNA silencing.
The unifying features of RNA silencing phenomena are the production of small 21β26 nt RNAs that act as specificity determinants for down-regulating gene expression Hamilton and Baulcombe ; Hammond et al. In animals, pre-miRNAs are transcribed as longer primary transcripts pri-miRNAs that are processed in the nucleus into compact, folded structures pre-miRNAs , then exported to the cytoplasm, where they are cleaved by Dicer to yield mature miRNAs Lee et al.
Here, we present evidence that extracts of wheat germ, introduced for the study of translation and protein translocation in the s Roberts and Paterson , recapitulate many of the key features of RNA silencing in plants.
Our inhibitor studies suggest that a different Dicer-like enzyme generates each siRNA class. Two distinct classes of small RNAs are produced in transgenic plants bearing silenced transgenes Hamilton et al. To test if the production of these two classes of small RNAs was a normal feature of plant biology or a specialized response to foreign DNA, we examined the length distribution of a nonredundant set of endogenous small RNAs cloned from Arabidopsis thaliana , including published sequences Llave et al.
Included in the set are known and predicted miRNAs, as well as small RNAs of unknown function corresponding to intragenic regions or to mRNA sequences in either the sense or antisense orientation. The distribution of lengths within this set was bimodal, with peaks at 21 and 24 nt Fig. In contrast, the length distribution of cloned small RNAs from C. The two classes are either generated by different enzymes, function in separate effector complexes, or both. Arabidopsis thaliana small RNAs form two distinct size classes.
