Sirna is a small RNA molecule that functions in gene silencing and post-transcriptional regulation. Sirnas are typically 21-23 nucleotides in length and can bind to complementary sequences on mRNA molecules, resulting in cleavage of the target mRNA or translational repression. Sirnas are involved in a variety of biological processes, including development, cell cycle regulation, stress responses, and viral defense.
Sirnas were first discovered in Caenorhabditis elegans by Richard J. Timmons and Victor R. Ambros in 1991 . The name sirna is derived from the C. elegans gene silencing mutant phenotype, which was termed “small interference” RNA. Since their discovery, sirnas have been found in a wide variety of organisms, including plants, fungi, animals, and viruses.
The biogenesis of sirnas involves several steps: transcription of primary sirna transcript (pri-sirna), processing of pri-sirna by Drosha/DGCR8 complex into pre-sirna molecules, export of pre-sirna to cytoplasm by Exportin 5/RanGTP complex, further processing of pre-sirna by Dicer into mature sirna duplexes. Mature sirnas associate with Argonaute proteins to form RNA-induced silencing complexes (RISCs). These complexes recognize complementary sequences on target mRNAs and mediate cleavage or translational repression.
Sirnas play important roles in various biological processes such as development,- cell cycle regulation,- stress responses,- viral defense.-, etc. In addition, aberrant expression or function of sirnas has been implicated in several diseases such as cancer,- Alzheimer’s disease , Huntington’s disease , etc.