Exogenous dsRNA, transposon, virus P P P P P P P P siRNAs + Ago RISC Ago RISC siRNA in RISC Cleavage of target mRNA Repeated cutting by dicer mRNA
DNA 2. RNA splicing Gene expression can be controlled by altering the rate of splicing in eukaryotes. Alternative splicing can produce multiple mRNAs from one gene. Mature RNA transcipt Exons Introns 5´ cap 3´ poly-A tail Cut intron RNA polymerase II 3´3´ 5´5´ Primary RNA transcript 1. Initiation of transcription Most control of gene expression is achieved by regulating the frequency of transcription initiation.
3. Passage through the nuclear membrane Gene expression can be regulated by controlling access to or efficiency of transport channels. 4. Protein synthesis Many proteins take part in the translation process, and regulation of the availability of any of them alters the rate of gene expression by speeding or slowing protein synthesis. 3´3´ 5´5´ Small subunit Nuclear pore 5´ cap mRNA Large subunit 3´ poly-A tail
23 5. RNA interference Gene expression is regulated by small RNAs. Protein complexes containing siRNA and miRNA target specific mRNAs for destruction or inhibit their translation. 6. Posttranslational modification Phosphorylation or other chemical modifications can alter the activity of a protein after it is produced. Completed polypeptide chain RISC P P