siRNA vs miRNA

SiRNA vs miRNA

Two classes of small RNAs, small interfering RNAs (siRNAs) and microRNAs (miRNAs), affect gene expression in animals and plants. They interfere with normal gene function on several levels, including promoter activity, mRNA stability, and translational efficiency. Small RNAs are the specificity components of a protein machinery known as RNA-induced silencing complex (RISC), which uses the small RNAs to recognize complementary motifs in target nucleic acids

Basic difference in siRNa and miRNA is that siRNA is a exogenous double stranded RNA taken up by cell, while miRNA is endogenous RNA molecule, encoded by specific miRNA gene and short haiprin pri-miRNA in the nucleus.  The siRNAs are cleaved from dsRNA by a class of RNase III enzymes known as Dicers (Bernstein et al., 2001 ). After cleavage, siRNAs from both strands can then target additional RNA molecules for degradation. Analogous to siRNAs are microRNAs (miRNAs) (Carrington and Ambros, 2003), a class of small RNAs differentiated from siRNAs by several features: nearly all miRNAs are complementary to sites within target mRNAs but generally contain one or more mismatches; miRNAs are processed from larger noncoding RNA precursors that contain stem-loop structures processed by a Dicer; and miRNAs are highly conserved in sequence, expression, and function. In plants, miRNAs act through several possible mechanisms: posttranscriptional cleavage of mRNA :inhibition of translation; and RdRP-mediated second-strand synthesis and trans-acting siRNA (ta-siRNA) production initiated by miRNA action .Cleavage of miRNA target genes has been documented regardless of mode of action. The prevalence of the putative translational block has not been assessed systematically and some evidence indicates that a transcriptional feedback mechanism may also be active