• In prokaryotes, no RNA processing is necessary:
the nascent RNA is usually the mRNA.
• In eukaryotes, the nascent RNA is called primary transcript-RNA
– needs to be processed
– and transported to the cytoplasm for translation to occur.
The processing steps are:
• RNA splicing
• nascent RNA controls transcription elongation .
• regulate RNA chain elongation .
• Expression of the human immunodeficiency virus type 1 (HIV-1)
• insight into the virus's mechanism for RNA synthesis.
• knowledge on the spatial distribution of transcriptionally active
post transcriptional gene silencing (PTGS)
• RNA molecules inhibit gene expression.
• Also known as co-suppression, post transcriptional
gene silencing (PTGS), and quelling.
• Initiation step:
1. Long double-stranded RNA
Dicer cleaves dsRNA to ~21 bp small interfering RNA
(siRNA), with 2nt 3’ overhangs
• Effector step:
1. Form RNA-induced silencing complexes (RISC)
2. siRNA guide RISC to target mRNA
3. RISC degrades target mRNA
siRNAs & miRNAs
These two classes of RNAs represent a subset of small
RNAs; both play important roles in gene regulation.
miRNAs and siRNAs cause inhibition of gene expression
• A microRNA (abbr. miRNA) is a small non-coding RNA molecule
• miRNAs are typically 21–25 nucleotides in length.
• Forms imperfect RNA-RNA duplexes.
• miRNA genes are usually transcribed by RNA polymerase II (Pol II). The
Tumor suppression and oncogenes
• About 50% of the annotated human miRNAs map within fragile sites
• evidence indicates that miRNAs can function as tumour suppressors
• Gene therapies that use miRNAs might be an effective approach
to block tumour progression
• The past several years have witnessed tremendous progress in our
understanding of miRNAs.
• Understanding how miRNAs are processed and how they are integrated into the
complex regulatory networks will be crucial.
• Considering the fundamental role of miRNAs in organismal development, cellular
differentiation and metabolism, viral infection, and oncogenesis, we can
anticipate many more sophisticated mechanisms for the regulation of their
biogenesis, function and catabolism to emerge in coming years.
• siRNAs are derived by the specific
nucleolytic cleavage of larger,
• 20-25 nucleotides long.
• short siRNAs usually form perfect
RNA-RNA hybrids with their distinct
targets potentially anywhere
within the length of the mRNA.
Both miRNAs and siRNAs represent exciting new potential
targets for therapeutic drug development in humans.
In addition, siRNAs are frequently used to decrease or
"knock-down" specific protein levels.
• Chemical synthesis.
• In vitro transcription.
- primary cells, suspension cells, and many difficult to transfected
• Viral vector
- most all type of cells, in vivo application
- long-term silencing
- adenovirus, lentivirus, retrovirus
• RNA interference (RNAi) has become an almost-standard method for in vitro
knockdown of any target gene of interest.
• The use of RNAi for therapeutic purposes holds a great deal of potential for the
treatment of viral and genetic diseases, and cancer.
• The specific aim of siRNA therapies is to control gene expression by gene silencing.
• RNA interference is a vital part of the immune response to viruses and other
foreign genetic material
• Although animals generally express fewer variants of the dicer enzyme than plants,
RNAi in some animals has also been shown to produce an antiviral response.
• In both juvenile and adult Drosophila, RNA interference is important in antiviral innate
immunity and is active against pathogens such as Drosophila X virus.
• A similar role in immunity may operate in C. elegans, as argonaute proteins are
upregulated in response to viruses and worms that overexpress components of the RNAi
pathway are resistant to viral infection.
• The widespread regulation of microRNA biogenesis, function and decay by Jacek Krol, Inga Loedige
and Witold Filipowicz.
• MicroRNA Functions by Natascha Bushati and Stephen M. Cohen.
• MicroRNA-9a ensures the precise specification of sensory organ precursors in Drosophila by Yan Li,
Fay Wang, Jin-A Lee, et al.
• Oncomirs — microRNAs with a role in cancer by Aurora Esquela-Kerscher and Frank J. Slack
• Molecular biology of the gene by Watson ,Baker,Bell,Gann,Levine,Losick (Sixth edition)
“Genes are the blueprints for Proteins, but Proteins are where the
action Is In Human Life and Health “
- Akhilesh Pandey