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