Nucleocytoplasmic traffic of non-coding
v In this chapter, we will look at how non-coding (nc) RNAs are
exported from the nucleus.
v Although mRNAs and ncRNAs follow the same route out of the
nucleus (via the nuclear pore), traffic is achie
Nucleocytoplasmic traffic of mRNA
v Eukaryotes are defined by the presence of a nuclear envelope
as well as other membrane-bound organelles (subcellular
v This spatial organization means that most cellular RNAs have to
v The ORFs of some RNAs can be altered after transcription by a
process called RNA editing.
v That is, RNA editing alters the sequence of transcripts without
affecting the sequence of their parent genes.
Why edit RNA?
v Why edit a t
How pre-mRNAs are decoded by the
v The spliceosome faces a considerable challenge.
1) Genes can be made up of relatively small exons separated by
huge stretches of intron.
2) The genome is also littered with sequ
RNA can form versatile structures
v Although RNA and DNA are made of similar building blocks, the
resulting molecules are quite different.
DNA is a linear double helix, while the RNA is much more
globular in structure.
In terms of the complexi
Stability and degradation of mRNA
v All macromolecules have variable stability, a characteristic that is
reflected by their half-life.
v The longer a molecules half-life, the greater its stability.
v Huge impact of a molecules stability on its
Translation of mRNA
v In this chapter, we cover the remarkable process of mRNA translation.
1) The structure of translation machinery (Ribosome and tRNA)
2) Three phases of translation: initiation, elongation, and termination
3) Regulation of m
Regulated RNA processing alternative
v There are ~30,000 genes in the human genome, but it is
estimated that at least 90,000 proteins are made by a typical
Alternative splicing acts as a multiplication factor which enables
The biogenesis of non-coding RNAs
v Maturation of non-coding RNAs during their biogenesis
These non-coding RNAs include rRNA, snRNA, tRNA, and RNA
component of telomerase (required for the formation of telomeres).
v The RNA processing machiner
v An essential part of the molecular architecture of cells is the
intracellular distribution of its components such as RNAs and
v It is important to localize mRNA in a particular cytoplasmic
location because a single
Long non-coding RNAs in epigenetic
v This chapter focuses on an important role of long non-coding RNAs in
v Epigenetics controls gene expression at transcription level.
v Epigenetic regulation involves
1) DNA m
Pre-mRNA splicing defects in
development and disease
v Some of the mutations affect how the genetic code is read, by
introducing codons for new amino acids and stop codons into
v Others affect splicing signals and so prevent the intron-ex
The RNA-binding proteins
v RNA-binding domains can recognize RNA sequences or
alternatively they can recognize RNA structures.
v RNA-binding domains can bind single-stranded RNA (ssRNA) or
double-stranded RNA (dsRNA).
Table 4.1 The known
v RNA molecules can catalyze chemical reactions, a domain
which was previously thought to be reserved only for proteins.
For example, RNA-processing reaction took place if highly
purified RNA was incubated by itself without any p
Co-transcriptional pre-mRNA processing
v Eukaryotic mRNA needs to be exported from the nucleus to the
cytoplasm prior to translation.
v In addition, there are several intervening steps b/w transcription
and the eventual translation of an mRNA in
The short non-coding RNAs and
v In this chapter, regulatory functions of small non-coding RNAs
(typically 21-30 nucleotides in length) will be discussed.
v Small ncRNAs act to guide protein components to complementary
Pre-mRNA splicing by the spliceosome
v A large proportion of eukaryotic genes are split into coding
segments (exons) separated by non-coding intervening
v Both the introns and exons in these split genes are transcribed