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Chromatin and DNA modifications vs RNA

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Compare the repressive effects of chromatin and DNA modifications with the repressive effects of RNAi. Including:
a) a basic overview of RISC and RITS repression
b) mechanisms or effects of RNAi that are similar or related to changes in chromatin
c) mechanisms or effects of RNAi that are unique

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The main difference between the negative regulation of gene expression mediated by the histone and DNA modifications and that controlled by the RNAi pathway is that the first type of regulation acts at the level of the DNA transcription, while the second type of regulation targets the mRNA stability and translation.

a) RISC and RITS repression, an overview

RISC (RNA induced silencing complex) repression starts with the production of the double-stranded RNA, which is cleaved by the enzyme called DICER generating short ~20 bp fragments, called siRNAs. These siRNAs are unwound into single strands: the passenger strand, which will be degraded and the guide strand that is integrated into the RISC complex. RISC complex consists of several protein components, and the active part of the RISC complex is represented by the endonucleases called argonaute proteins. The argonautes cleave the target mRNA complementary to their bound guide RNA ...

Solution Summary

The solution addresses the mechanisms of gene regulation at two different levels: 1. DNA and chromatin modifications and 2.RNA interference. Specifically, we discuss the general principles of RISC and RITS repression and then compare these to the mechanisms of gene repression at the level of DNA and chromatin modifications.

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Explain the relationship between chromatin packaging and transcription rates. Name two different types of chromatin modification associated with changes in gene expression. Indicate how the DNA or protein is modified chemically and how the modification affects the chromatin structure (that is, does the modification relax or compact chromatin? Is the modification associated with active or inactive chromatin?)

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