When I read DRACO paper, my adviser ask me the question (on the title).
My primitive idea is the following text. (2011.08)
On the beginning, I also send a letter to Dr. Rider, but I didn’t receive his reply
This question can be divided into two parts: one is why viruses produce long dsRNAs, the other is why endogenous dsRNAs are short.
In August,I guess endogenous long dsRNA is unstable in cells.Dicer can cleaves endogenous dsRNAs to produce siRNA. Long endogenous dsRNAs can induce complete Gene silencing in mammalian cells and primary cultures. So endogenous dsRNA are shorter than exogenous dsRNA.
But, there are some questions on my guess.
What RNA belong to dsRNA?
As we know, mircoRNA is not siRNA, though it as little as siRNA. So, what RNA is dsRNA? tRNA and rRNA has some hairpin structure (cloverleaf structure). Does this structure is double strand structure? All RNA viruses must produce at least a transient dsRNA intermediate. In replicating + or - RNA, you have to produce the opposite sense RNA, thus forming a dsRNA molecule. tRNA has only one strand, and the hairpin structure isn’t made of double strands.
I think dsRNA must made of two strands perfectly complementary, the secondary structure isn’t reflect strand type.
On the molecular biology class, I learn mircoRNA is single strand. (2011.10.14)
Why endogenous dsRNAs are short?
In the DRACO paper, it said that uninfected mammalian cells don’t produce long dsRNA. Information generally transfer from DNA to RNA (central dogma). RNA can not replication in human cells.So endogenous dsRNAs are not existence in human cells.
Why viruses produce long dsRNAs but not short ones?
RNA viruses’ genetic information are all in the RNA, so it longer.
However, I think I have misunderstanding the question. (2011.10.09)
Why viruses produce dsRNAs?
Positive-strand RNA, dsRNA, or DNA viruses produce dsRNA.
RNA polymerase synthesizes an RNA strand complementary to the genome. This produces a dsRNA. RNA can not replication in human cells.So endogenous dsRNAs are not existence in human cells.
Negative-strand RNA viruses doesn’t produce dsRNA. (Double-Stranded RNA Is Produced by Positive-Strand RNA Viruses and DNA Viruses but Not in Detectable Amounts by Negative-Strand RNA Viruses)