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  • Front
  • Back
RNA has to undergo modifications before proteins can be
translated
Eukaryotes have Separate compartments for
transcription and translation
RNA polymeraseII has ____subunits
12
Types of eukaryotic RNA
mRNA: messenger RNA
–Template for protein synthesis (i.e. translation)
•tRNA: transfer RNA
– carries amino acids to the ribosome
•rRNA: ribosomal RNA
–Major component of ribosome and plays a structural and functional role
transcribes 18S, 5.8S and 28S rRNA
RNA polymerase I
transcribes mRNA other snRNAs
RNA polymerase II
transcribes 5S rRNA and all tRNA
RNA polymerase III
-aminitin (produced by the poisonous mushroom Amanita phalloides) strongly inhibits RNA polymerase___
RNA polymerase II
Processing of mRNA transcript requires:
•5‟ cap
•3‟ polyA tail
•Splicing
7-Methylguanosine, m7Gppp is?
5´-CAP Structure of Eukaryotic mRNA
Transcript termination involves the addition of
a poly(A)250 tail.
mRNA transport
Mature mRNA is transported out of the nucleus to be translated in the cytoplasm.
•Proteins build based upon the code on mRNA
Genes coding for proteins comprise of only___ of the human genome.
2%
The half-life of mRNA is an important determinant of gene expression since
the amount of time an mRNA can be translated will also determine the amount of protein product made
The half-life of an mRNA also determines how
rapidly the synthesis of the encoded protein can be shut down after transcription ceases.
of mRNA is achieved by the coordinate interactions between an RNA‟s structural components and specific trans-acting factors (RNA binding proteins).
The regulated decay
Different mRNAs can be degraded via
distinct pathways while a given mRNA can also be degraded by different, seemingly-redundant pathways, depending upon cellular conditions.
mRNA structural components include
5‟-Cap structure
5‟-UTR
Protein coding region
3‟-UTR
3‟-Poly(A) tail
mRNA decay pathways
•Deadenylation dependent pathway
•Deadenylation independent pathway
•Nonsense mediated decay
•mRNA instability elements
In the Deadenylation-Dependent Pathways that have been characterized
poly(A) shortening is followed by decapping and both 5„3' and 3„5' exonucleolytic decay.
Some mammalian mRNAs (like insulin-like growth factor 2 (IGF2) and transferrin receptor (TfR)) are degraded by endonucleolytic activities independent of deadenylation.
Following endonucleolytic cleavage, the resulting 5'-fragment is targeted for 3„5' degradation activity (vulnerable 3'-OH end), while the 3'-fragment may be a substrate for a 5„3' degradation activity (vulnerable 5'-end).
Transcripts that harbor nonsense codons, unspliced introns or extended 3'-UTRs are targets for the NMD pathway.
In yeast, this pathway involves deadenylation-independent decapping followed by 5„3' degradation. At this point, the sequence of degradation steps involved in NMD in mammalian cells is unknown.
What Are mRNA Instability Determinants?
A + U-Rich Elements (AREs)
The ARE’s have been recognized as a potent destabilizing elements in a wide variety of short-lived mRNAs like those of proto-oncogenes and cytokines. The A + U-rich motif, located in the 3'-UTR of mRNAs is described by a variable number of overlapping AUUUA pentamers, frequently harbored in or about a U-rich region.
The 5'-UTR can play significant roles in altering stability either in
a translation-dependent manner by containing translation-inhibiting stem-loops, or in a manner independent of translation.
prevents the translation of defective -globin mRNAs.

Important in modulating the severity of -thalassemia phenotype (NMD)
mRNA stability mechanisms and surveillance
A posttranscriptional modification resulting in an alteration of the primary nucleotide sequence of RNA transcripts by a mechanism other than splicing. The process may involve the modification, insertion, deletion, or substitution of nucleotides in the RNA molecule.
RNA EDITING
ROLES OF RNA EDITING:
mRNA translation
pre-mRNA splicing
RNA Degradation
RNA Replication
RNA Structure
Mechanism of Apolipoprotein B mRNA Editing
makes two different proteins, ApoB48 in the intestine and ApoB100 in the Liver. Due to the Cytidine Deaminase Editing Complex (ACTIVE) in the intestine.
are ~20nt long RNAs
•Formed from larger double stranded or hairpin structure RNAs by an cytoplasmic endonuclease DICER.
•miRNA binds to complementary mRNA with the aid of RNA-induced silencing complex (RISC)
•The imperfect miRNA-mRNA duplex represses translation.
miRNA
miRNA applications
* cell death and cell proliferation.
* many of which are involved in initiation and progression of cancer
* developed for targeting specific genes to turn off their translation e.g. for BCL-2 oncogene, PTEN tumor suppressor etc.
siRNA (RNAi)
complementary to mRNA.
The siRNA-mRNA complex results in cleavage and inactivation of the target mRNA.
•The RISC endonuclease which cleaves the mRNA is called SLICER.
siRNA applications
siRNA can be custom-synthesized to target your favorite gene
•Widespread use in disease models of diabetes, neurodegenerative disease, metabolic disorders etc.
•In vivo application issues such as stability, efficacy and delivery methods.
Short hairpin RNAs (shRNAs)
packaged into a vehicle- usually recombinant human or non-human virus.
•Advantages:
–Choice of viral vector provides a high degree of efficacy and specificity
–Many viral vectors are already approved for clinical trials
–The shRNAs are control of the promoter of the viral vector and hence its expression can be regulated.
is a process by which genetic information is transferred into a functional protein.
Gene expression