Viruses and RNA interference in mammalian cells
Viruses and RNA interference in mammalian cells
Viruses and RNA interference in mammalian cells
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L<strong>in</strong>k between mi<strong>RNA</strong>, si<strong>RNA</strong> <strong>and</strong> <strong>RNA</strong>i (si<strong>RNA</strong> versus mi<strong>RNA</strong>)<br />
Both mi<strong>RNA</strong>s <strong>and</strong> si<strong>RNA</strong>s trigger <strong>RNA</strong> silenc<strong>in</strong>g, the repression of specific sequences of<br />
m<strong>RNA</strong>. The si<strong>RNA</strong>s are equivalent to mi<strong>RNA</strong>s (Montanucci et al., 2005). Mi<strong>RNA</strong>s as well<br />
as si<strong>RNA</strong>s belong to the small <strong>RNA</strong> class. It is supposed, that they differ only <strong>in</strong> their<br />
biogenesis: mi<strong>RNA</strong>s orig<strong>in</strong>ate from short hairp<strong>in</strong> <strong>RNA</strong> (sh<strong>RNA</strong>, also called micro <strong>RNA</strong><br />
precursors, pre-mi<strong>RNA</strong>), produced by Drosha. Si<strong>RNA</strong>s are cleaved from ds<strong>RNA</strong>s by Dicer<br />
(Carmell <strong>and</strong> Hannon, 2004). Mature mi<strong>RNA</strong>s are ss<strong>RNA</strong> molecules, 21 or 22 nt <strong>in</strong> length,<br />
that are endogenously produced. However, si<strong>RNA</strong>s are ds<strong>RNA</strong> molecules 21-25 nt long <strong>and</strong><br />
can be endogenous as well as exogenous (Aagaard <strong>and</strong> Rossi, 2007; Carmell <strong>and</strong> Hannon,<br />
2004; Elbashir et al., 2001). The perfect match recognition (complementary with targeted<br />
<strong>RNA</strong>) sequences for mi<strong>RNA</strong> can be 7-8 nt <strong>and</strong> the complete sequence permit mismatches,<br />
not as si<strong>RNA</strong>s (Zeng et al, 2003). Endogenous si<strong>RNA</strong>s are rarely conserved <strong>in</strong> related<br />
organisms that is not the case for mi<strong>RNA</strong> sequences (Lee et al., 2003). Endogenous si<strong>RNA</strong><br />
specify “auto-silenc<strong>in</strong>g” <strong>in</strong> that they silence the same locus or a very similar loci from which<br />
they orig<strong>in</strong>ate, whereas mi<strong>RNA</strong> specify “hetero-silenc<strong>in</strong>g”, they are directed for silenc<strong>in</strong>g<br />
different genes (He <strong>and</strong> Hannon, 2004).<br />
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