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Author: Stephen Jones
RNA interference (RNAi) is the process of mRNA degradation that is induced by
double-stranded RNA in a sequence-specific manner. RNAi has been observed in all
eukaryotes, from yeast to mammals. The RNAi pathway is thought to be an ancient
mechanism for protecting the host and its genome against viruses and rogue
genetic elements that use double-stranded RNA (dsRNA) in their life cycles. They
have also been shown to play a role not only in mRNA and dsRNA
stability/degradation, but also in regulation of translation, transcription,
chromatin structure, and genome integrity. In plants and animals, RNA silencing
has been adapted to play a critical role in regulation of cell growth and
differentiation using a class of small RNAs. In the RNA interference process,
the dsRNAs get processed into 20-25 nucleotide (nt) small RNAs by an RNase
III-like enzyme called Dicer. Then, the small RNAs assemble into
endoribonuclease-containing complexes known as RNA-induced silencing complexes
(RISCs), unwinding in the process. The small RNA strands subsequently guide the
RISCs to complementary RNA molecules, where they cleave and destroy the cognate
RNA (effecter step). Cleavage of cognate RNA takes place near the middle of the
region bound by the siRNA strand. The small RNAs that provide target specificity
to the silencing machinery includes short interfering RNAs (siRNAs),
repeat-associated siRNAs (rasiRNAs), and microRNAs (miRNAs) and is distinguished
by their origin. siRNAs are processed from dsRNA precursors made up of two
distinct strands of perfectly base-paired RNA, while miRNAs originate from a
single, long transcript that forms imperfectly base-paired hairpin structures.
siRNAs were originally identified as intermediates in the RNAi pathway after
induction by exogenous dsRNA; however, endogenous sources of siRNAs have now
been recognized. The endogenous siRNAs are derived from repetitive sequences
within the genome, and are termed repeat-associated siRNAs, or rasiRNAs. miRNAs
were discovered through their critical roles in development and cellular
regulation, and represent a large class of evolutionarily conserved RNAs. miRNAs
have always been recognized as being of endogenous origin. RNA interference has
emerged as a natural mechanism for silencing gene expression over the past
decade. This ancient cellular antiviral response can be harnessed to allow
specific inhibition of the function of any chosen target genes, including those
involved in causing diseases such as cancer, AIDS, and hepatitis. It is already
proving to be an invaluable research tool, allowing much more rapid
characterization of the function of known genes. More importantly, the
technology considerably bolsters functional genomics to aid in the
identification of novel genes involved in disease processes. Last but not the
least the technology can be harnessed as a novel therapeutic agent and is
suitable for combating viral diseases, cancers and inflammatory diseases.
Imgenex (San Diego) recently launched the pSuppressorAdeno construction kit for
adenovirus mediated gene knockdown. The kit provides the ability to infect a
broad range of cell types, including many primary cell lines as well as dividing
and nondividing cells, according to a company official. The kit also offers the
flexibility to validate sequences using the nonviral expression plasmid prior to
construction of adenoviruses, notes Sujay K. Singh, Ph.D., president and CEO of
Imgenex, which markets plasmid-based RNA interference (RNAi) products. "One of
the greatest advantages is the ability of recombinant adenovirus vectors to
reduce gene expression both in vitro and in vivo," he adds. RNAi, initially
considered a bizarre attribute of petunias and later a gene-silencing mechanism
in worms, is creating a stir as one of the hottest new technologies in molecular
biology. It is revolutionizing the field of functional genomics.
IMGENEX India Pvt Ltd. the only biotech company in Orissa and one of its
kinds in Eastern India. IMGENEX India started in Oct as an outsourcing branch of
IMGENEX Corporation, San Diego, USA.
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