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CH 20: Regulatory RNAs (A. Regulation by RNAs in Bacteria (Riboswitches…
CH 20: Regulatory RNAs
A. Regulation by RNAs in Bacteria
Riboswitches reside within the transcripts of genes whose expression they control through changes in secondary structure
RNAs as defense against agents in prokaryotes and archaea
CRISPRs are a record of infections survived and resistance gained
Spacer sequences are acquired from infecting viruses
A CRISPR is transcribed as a single long RNA, which is then processed into shorter RNA species that target destruction of invading DNA or RNA
B. Regulatory RNAs are Widespread in Eukaryotes
Short RNAs that silence genes are produced from a variety of sources and direct the silencing of genes in three different ways
C. Synthesis and Function of miRNA Molecules
miRNAs have a characteristic structure that assists in identifying them and their target genes
An active miRNA is generated through a two-step nucleolytic processing
Dicer is the second RNA-cleaving enzyme involved in miRNA production and the only one needed for siRNA production
D. Silencing Gene Expression by Small RNAs
Incorporation of a guide strand RNA into RISC makes the mature complex that is ready to silence gene expression
Small RNAs can transcriptionally silence genes by directing chromatin modification
RNAi is a defense mechanism that protects against viruses and transposons
RNAi has become a powerful tool for manipulating gene expression
E. Long Non-coding RNAs and X-inactivation
Long non-coding RNAs have many roles in gene regulation, including Cis and Trans effects on transcription
X-inactivation creates mosaic individuals
Xist is a long non-coding RNA that inactivates a single X chromosome in female mammals