RNA silencing – a play in three acts: three examples of RNA silencing (Here is an outline I have used before – read over the lecture material and think about what role you might like to play; roles are indicated in bold- this might be in class Thursday or Monday) Act 1 – Transcriptional gene silencing or How the desire for darker petunias led to fame, but not fortune. Scientists add a transgene to the genome of the petunia. This gene codes for chalcone synthase, an enzyme in the anthocyanin biosynthetic pathway. The petunia genome also includes endogenous genes for chalcone synthase . These genes are present in euchromatin. The transgene is transcribed into mRNA – in this case it represents transcript from repetitive DNA . This transcript is used by RdRp to synthesize dsRNA . The dsRNA is cleaved by Dicer into short pieces of RNA, siRNA . The siRNA forms a complex – RISC , that is partially responsible for chromatin modification – here from euchromatin to heterochromatin. Thus both endogenous and
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