i am also working on the same issues, but idea is that this dsRNA is encoded by the repeated sequence so when transcribed it forms shRNA (Short hairpin loop RNA) that is further processed into small interfering RNA (siRNA). But this is one explaination there may be some otheres.
if you find some other, please also tell me.
aftab ahmad [Only registered users see links. ]
I found some very interesting information. It seems not much is known about the coding of dsRNAs and RNai molecules.
See: [Only registered users see links. ]
miRNA and RNAI molecules are transcribed by RNA polymerase II:
MicroRNA genes are transcribed by RNA polymerase II
Yoontae Lee1, Minju Kim1, Jinju Han1, Kyu-Hyun Yeom1, Sanghyuk Lee2, Sung Hee Baek1 and V Narry Kim1
Here we present the first direct evidence that miRNA genes are transcribed by RNA polymerase II (pol II). The primary miRNA transcripts (pri-miRNAs) contain cap structures as well as poly(A) tails, which are the unique properties of class II gene transcripts.
Estimates suggest that 200–300 unique miRNA genes are present in the genomes of humans and mice (Lim 2003 b). The sequences of many of the miRNAs are homologous among organisms, suggesting that miRNAs represent a relatively old and important regulatory pathway (Grosshans 2002).
Most of the genome sequences encoding miRNAs occur in areas of the genome that are not associated with known genes; many are found in fragile sites in human chromosomes (Calin 2004) and appear to be independently transcribed (Lagos-Quintana 2001, Lau 2001, Lee 2001, Lim 2003a, 2003b). A number of miRNAs, are encoded in introns of primary mRNA transcripts. Typically they are encoded in the same orientation as the parent transcript, indicating that transcription of this class of miRNA gene is driven by an mRNA promoter (Aravin 2003, Lagos-Quintana 2003, Lai 2003, Lim 2003a). Unlike C. elegans and human, in Drosophila, most miRNA genes are found as clusters in the genome. There is good evidence that these clustered miRNA genes are expressed as multi-cistronic transcripts which are then processed to become mature miRNAs.