Regulatory RNAs

RNA DNA mRNA rRNA tRNA snRNA snoRNAmicroRNA siRNAribozymes Protein synthesis Splicing of mRNA Processing of rRNA Regulation of gene expression Catalysts

Whole genome studies Tiling assays

Bacterial sRNAs bind to mRNAs and trigger degradation or regulate translation

Riboswitches and attenuation are mechanisms to control gene expression in bacteria Organization of a riboswitch

Example: a SAM riboswitch Termination of transcriptionRepression of translation initiation

Example: a SAM riboswitch Transcriptional terminator

Examples of riboswitches and their metabolites

Attenuation is used in bacteria to regulate transcription of biosynthetic genes The leader peptide contains trp amino acids

Attenuation is used in bacteria to regulate transcription 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.coliP. furiosus

Gene-editing using the CRISPR-Cas9 system Animation Animation1

RNA DNA mRNA rRNA tRNA snRNA snoRNAmicroRNA siRNA piRNAs ribozymes Protein synthesis Splicing of mRNA Processing of rRNA Regulation of gene expression Catalysts

In eukaryotes short RNAs are generated by mechanisms that are different from the mechanisms that generate sRNAs in bacteria. RISC: RNA-induced silencing complex Bacterial sRNAs are encoded by small genes whereas eukaryotic small RNAs are processed from longer transcripts.

The PIWI-interacting RNA (piRNA) system is thought to silence transposons by passively acquiring and expressing transposon sequences

Processing and function of microRNAs and siRNAs RISC: RNA-induced silencing complex

Pre-microRNAs can originate from various regions of a primary transcript (pri-miRNA)

Structures of pre-microRNAs in Caenorhabditis

General structure of a pri-microRNA and its processing sites

Processing of pri-microRNAs by Drosha in the nucleus Microprocessor complex Pasha, Pre-miRNA (F2) is transported into the cytoplasm

Dicer processes microRNAs in the cytoplasm PAZ: PIWI, argonaute, zwille

General structure of a pri-microRNA and its processing sites

Argonaute (as part of a RISC complex) cleaves mRNAs after complementary base pairing of its guide RNA.

In eukaryotes short RNAs are generated by different mechanisms 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 inhibitory effect

Repressing gene expression by RNAi in Caenorhabditis

X-chromosome inactivation is initiated by expression of the Xist gene from the X-chromosome inactivation center (Xic) Xist: X-inactive specific transcript Long non-coding RNAs (lncRNAs), longer than 200 nucleotides Regulatory elements

Visualizing the Xist lncRNA (a) and the acetylation state of one of the X-chromosomes (b)

Calico cats have patch-colored fur due to expression of different X-chromosome alleles