Question

Outline the steps that occur when piRISCs silence transposable elements by repressing transcription and by directly inhibiting TE RNAs. What is the role of piRNAs in this process?

Short answer

piRISCs silence transposable elements through a dual approach: transcriptional repression and direct inhibition of TE RNAs. Transcription repression alters the epigenetic environment, thus preventing transcription initiation. Direct inhibition degrades the TE RNAs, preventing the transposable elements from causing mutations. piRNAs determine the target specificity of the response by guiding piRISCs to their target sites, being an essential component of these complexes.

Step-by-step solution

Explain what piRISCs are

piRISCs (Piwi-interacting RNA-induced silencing complexes) are molecular complexes that function in the repression of transposable elements. They move along with their complementary RNA hereditary material and degrade it to perform the function of silencing.

Outline the transcription repression by piRISCs

In transcription repression, piRISCs achieve silencing of transposable elements by creating an epigenetic environment that does not favor transcription. This process changes the methylation of DNA and the acetylation of histones affecting the chromatin structure, which prevents the initiation of transcription.

Describe the direct inhibition of TE RNAs by piRISCs

piRISCs also silence transposable elements by direct inhibition of TE RNAs. Once the piRISCs bind to their target RNA, they cleave and degrade it. This direct inhibition prevents transposable elements from moving and causing possibly harmful mutations.

Explain the role of piRNAs

piRNAs, or Piwi-interacting RNAs, are small non-coding RNAs that are essential components of piRISCs. They determine the specificity of the response since they are complementary to the transposable element sequences in the RNA. The piRNA sequence thus determines which transposons are silenced by guiding the piRISCs to their target sites.