Regulatory RNAs
Bacterial sRNAs bind to mRNAs and trigger degradation or regulate translation
Riboswitches and attenuation are mechanismsto control gene expression in bacteria
Organization of a riboswitch
Example: a SAM riboswitch
Termination of transcription Repression of translation initiation
Example: a SAM riboswitch
Transcriptional terminator
Examples of riboswitches and their metabolites
Attenuation is used in bacteria to regulatetranscription of biosynthetic genes
The leader peptidecontains trp aminoacids
Attenuation is used in bacteria to regulatetranscription of biosynthetic genes
Bacterial defense against viruses: The CRISPR system
CRISPR: Clustered Regularly Interspaced Short Palindromic Repeats
Organization of a CRISPR locus
Organization of CRISPR-associated genes in bacteria
CRISPR locus
Acquisition of spacer sequences
PAM: protospacer adjacent motif
Processing of CRISPR RNA and its antiviral action
E.coli P. furiosus
Gene-editing using the CRISPR-Cas9 system
Animation
In eukaryotes short RNAs are generated by differentmechanisms than sRNAs in bacteria
RISC: RNA-induced silencing complex
The PIWI-interacting RNA (piRNA) system is thought tosilence transposons by passively acquiring and expressingtransposon sequences
In eukaryotes short RNAs are generated by differentmechanisms than sRNAs in bacteria
RISC: RNA-induced silencing complex
Pre-microRNAs can form from various regions of a transcript
Structures of pre-microRNAs in Caenorhabditis
General structure of a primary microRNA andprocessing sites
Processing of pri-microRNAs by Drosha in the nucleus
Dicer processes microRNAs in the cytoplasm
Argonaute cleaves mRNAs after complementary base pairingof its guide RNA
In eukaryotes short RNAs are generated by differentmechanisms than sRNAs in bacteria
RISC: RNA-induced silencing complex
Centromeric silencing in S. pombe involves RNAi
Short interfering RNAs can be copied by an RNA-dependent RNA polymerase to amplify the inhibitoryeffect
Repressing gene expression by RNAiin Caenorhabditis
X-chromosome inactivation is initiated by expression of the Xist gene from the X-chromosome inactivation center (Xic)
Visualizing the Xist lncRNA (a) and the acetylation state of oneof the X-chromosomes (b)
Calico cats have patch-colored fur due to expression of differentX-chromosome alleles
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