Viruses and RNA interference in mammalian cells

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RNA synthesis. It destructs the RNA transcripts (De Carvalho et al., 1992 ; Van Blokland et al., 1994). RNAi was first described in 1998 when the researchers found that gene interference produced by dsRNAs was considerably more effective than were sense or antisense strand separately. Moreover, the introduction of specific dsRNA sequences in minimal quantities into the nematode Caenorhabditis elegans could effectively silence the expression of a target gene in the injected animals, as well as in their progeny (Fire et al., 1998). General RNAi mechanism DsRNA (more than 30 bp) is produced from the invading genes, either during viral replication or by aberrant transcription from promoters located near the transgene insertion site. Initiative dsRNA can be either exogenic or endogenic. RNAi is carried out in two steps (Figure 3). Frst, long dsRNA homologous in sequence to the silenced gene (Elbashir et al., 2001) is converted to 21–23-nucleotide small interfering RNA (siRNA) duplexes by ribonuclease III (RNase III)-like enzyme Dicer in the cytoplasm (Meister and Tuschl, 2004). In the second step, the small dsRNA products of the cleavage are assembled into a multiprotein RNA-induced silencing complex (RISC) with the help of the Dicer in the cytoplasm. Then the duplexes of siRNA unwound and one single (Nykanen et al., 2001; Martinez et al., 2002) strand with lowest stability at its 5’-end (Schwarz et al., 2003), guides RISC to its complementary mRNA. Further, mRNA is degraded by RISC nuclease activity. As a result, the translation stops (Elbashir et al., 2001). The other anti-guide strand is degraded during RISC activation (Gregory et al., 2005). Below, more detailed description of RNAi functional elements is given. 8
Figure 3. RNAi mechanism. RNAi is triggered by siRNAs, which are located in cytoplasm. Either dsRNA or small hairpin RNA (shRNA) are their precursors, cleaved by Dicer in ATP-depending manner. The siRNA sequences associated with RISC unwind also in ATP-depending manner. This complex recognizes target mRNA and degrades it, releasing RISC. (Rutz and Scheffold, 2004) RNAi functional elements siRNAs are small RNAs formed through cleavage of long dsRNA molecules, with complementary nucleotide sequences to the targeted RNA strand. They are 20–25 (21–25 nt in plants) nucleotides in length and they usually have a two-base overhang on the 3' end, 9
Page 1 and 2: UNIVERSITY OF TARTU FACULTY OF SCIE
Page 3 and 4: ACRONYMS AND ABBREVIATIONS CrPV - C
Page 5 and 6: LITERATURE OVERVIEW 1. Intracellula
Page 7: RNAi The development of biotechnolo
Page 11 and 12: Figure 4. Dicer components. 2 helic
Page 13 and 14: Link between miRNA, siRNA and RNAi
Page 15 and 16: 3. RNAi as an antiviral defense in
Page 17 and 18: 4. RNA interference in mammals The
Page 19 and 20: diseases, including liver cirrhosis
Page 21 and 22: esponse by suppressing the activity
Page 23 and 24: CONCLUSIONS In the present bachelor
Page 25 and 26: REFERENCES Aagaard, L. and Rossi, J
Page 27 and 28: Gitlin, L., Karelsky, S. and Andino
Page 29 and 30: Li, W.X. and Ding, S.W., (2001) Vir
Page 31 and 32: Schütz, S. and Sarnow, P. (2006) I

Viruses and RNA interference in mammalian cells

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