Download Dr. Peter John M.Phil, PhD Assistant Professor National University of

Dr. Peter John
M.Phil, PhD
Atta-ur-Rahman School of Applied Biosciences (ASAB)
National University of Sciences & Technology (NUST)
RNA Splicing & Processing
Alternative splicing
 Alternative Splicing: When a single gene give rise
to more than one type of mRNA
 Use
of
different
start
points/
generation
of
alternative 3’ ends alter the pattern of splicing
 In some cases the multiple products are made in the
same cell but in other the splicing is normal
Alternative splicing
 An alternative splicing pathway uses another set of
snRNPs that comprise the U12 spliceosome.
 The target introns are defined by longer consensus
sequences at the splice junctions, but usually include
the same GU-AG junctions.
 Some introns have the splice junctions AU-AC,
including some that are U1-dependent and some that
are U12-dependent.
Alternative Splicing in E1A
 Adeno virus E1A region by using alternative 5’ sites
generates different size products
 T antigen is larger in size
 t antigen is smaller in size
Alternative Splicing in E1A
 t antigen producing cell
 From these cell extract protein ASF (Alternative
Splicing factor)
 This protein (ASF) (alternative splicing factor) have
same role as splicing factor SF2, required for early
steps in spliceosome assembly and for the first
cleavage-ligation reaction
Alternative Splicing in Mouse
 Exon 2 & 3 of the Mouse Tropnin T gene are
mutantly exclusive
 Exon-2 used in smooth muscle & Exon -3 used in
other tissue
 Smooth
muscle contain protein that binds to
repeated elements located on either side of the exon3 & prevent use of the 3’ & 5’ sites that are needed to
include it
Drosophila Sex Determination
 Male include exon-3 of sxl gene which have
termination ultimately no SXL protein
 Female exclude exon-3 of sxl gene
 SXL protein in female
 SXL protein change the splicing of Tra gene
 Tra produce Tra2 gene
 Tra + Tra 2 produce dsx (double sex) gene
 DSX protein suppress male genes & promote
female development
Drosophila Sex Determination
 Sex determination in D. melanogaster involves a
pathway in which different splicing events occur in
females.
 Blocks at any stage of the pathway result in male
development.
Splicing and mRNA export
 Spliceosome also may provide the initial point of
contact for the export apparatus.
 A protein complex binds to the RNA via the splicing
apparatus
 The complex consists of >9 proteins and is called the
EJC (exon junction complex)
Exon Junction Complex EJC
 EJC is involved in several functions
 Some of the proteins of the EJC are directly involved
in association with splicing Factors
 Others recruit additional proteins for particular
functions
mRNA Transport
 EJC includes a group of proteins called the REF
family
 REF proteins in turn interact with a transport
protein (called TAP and Mex)
 TAP and Mex has direct responsibility for interaction
with the nuclear pore
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