Les V

at transcriptional level

waar gebeurt de meeste regulatie van expressie?

Role of transcription factors

Modulated by DNA methylation, histone modifications, chromatin structure

hoe gebeurt regulatie van expressie op transcriptional level?

RNAi: suppression of mRNAs by the action of double- stranded small non-coding RNA.

meest bekende voorbeeld van post-transcriptional regulation

upstream ORFs

heel bekend voorbeeld translational regulation

uORFs clearly shorter, in the 5’UTR. The ribosomes can accumulate here, leading to ‘stalling’ of the ribosomes, which has a negative effect on further translation of the main ORF, so a WEAKENING process. Not present in all!

werking uORFs als translational regulation

miRNA

siRNA

belangrijke ncRNAs voor gene regulation en silencing

Viral RNA (dsRNA) gets degraded in the youngest leaves of tobacco to siRNAs

ontdekking RNAi in plants

an RNAse III enzyme that cuts dsRNA in small RNAs called siRNAs

DICER

20-24 bp

lengte DICER

gets integrated in RISC

wat gebeurt er met siRNAs, nadat ze gemaakt zijn uit dsRNA

RNA-induced silencing complex

RISC

Argonaute (AGO)

main protein in RISC

1/ a miRNA-gene is transcribed into a primary miRNA

2/ processing –> pre-miRNA -> export to cytoplasm

3/ cleaved by Dicer -> mature miRNA (ca. 21 nt)

4/ miRNA is integrated in RISC -> silencing of target mRNA

werking miRNAs

In the continuous fight between host cells and pathogens, viruses have evolved proteins that suppress RNAi.

virussen en silencing

Individual gene with its own TSS

miRNA cluster with one shared TSS

mirtron : microRNA located in intron (transcribed with the host gene)

3 opties van miRNA genes in het genome

miRNA often target mRNAs encoding receptors, kinases, TFs

waarop werken miRNAs vaak?