Lecture 7: Examining Post-translational regulation
**Notes only make sense when read alongside the lecture slides
posted on Blackboard**
October 1, 2013
scientists can examine the entire proteome of a cell.
2 dimensional gel electrophoresis fig 7-4 on slide
each spot represents different proteins
proteomes different in 2 tissues (brain and liver)
a lot of this attributable to post transcriptional and post
since there is translational and post-translational regulation,
RNA can be different but that doesn't necessarily mean that the
protein will be different. because there are regulatory steps at
so many levels.
translational control very rapid.
mRNAs have six nucleotide Shine-Dalgarno sequence
AUG codon is where translation will initiate
shine-Dalgarno required for efficient translation. it correctly
positions AUG codon in the ribosome.
much of translational control mechanisms revolve around having
access to shine-Dalgarno sequence
PROKARYOTES: MECHANISM TRANSLATIONAL REGULATION 1
RNA binding protein blocks access to SD sequence.
translational repressor protein blocks access to SD sequence by
binding to it
how RNA molecules can adapt secondary structures. by interacting
with different sequences found in RNA molecules. single stranded
RNA molecules fold up in elaborate ways to form base pairing.
RNA interacting with itself at the stem. stem is red and blue (on
PROKARYOTUIC MECHANISM TRANSLATIONAL REGULATION 2:
listeria monocytogenes causes listeriosis.
its proteins expressed under specific conditions: regulated by
RNA structures that are temperature regulated. RNA molecules adapt a stem loop structure under 30C so that SD
sequence is not accessible.
but when temp above 30C stem loop melts and there is exposure of
SD sequence, therefore virulence proteins expressed.
pathogen only expressed when inside host.
PROKARYOTUIC MECHANISM TRANSLATIONAL REGULATION 3:
when a small molecule binds to RNA, it can cause structural
rearrangement of the RNA, blocking the SD sequence.
SD no longer accessible
when no small molecule bound, SD exposed and protein is expressed
riboswitches either turn translation on or off depending on how
it binds to RNA and alters its structure
PROKARYOTUIC MECHANISM TRANSLATIONAL REGULATION 4:
antisense RNA binds to RNA molecule and overlaps with SD.
therefore, SD becomes inaccessible to ribosome. therefore, no
translation. a base pairing interaction - so antisense RNA must
be complimentary to RNA.
antisense RNA coded in genome and then goes and binds to other
RNAs, genome regulates its own translation
TRANSLATIONAL REGULATION IN EUKARYOTES:
no SD sequences that regulate translation
but similar repressors that bind to start codon near AUG
(initiator) and therefore interfere with translation initiation
i.e.: cytosolic aconitase regulating expression of ferritin.
ferritin not needed when iron low in cell; only needed when iron
is high in body.
cytosolic aconitase is an iron binding molecule. it undergoes a
conformational change when it binds to iron. therefore, it can
directly sense iron.
repressor proteins can also interfere with 5' cap and 3' poly-A
tail. these 2 things required for efficient translation.
there are repressor proteins that interfere with translation
factors interacting with cap and tail. there are small RNA molecules that can regulate eukaryotic
when there is not extensive RNA matching, RNA becomes p-bodies.
therefore, translation of RNAs reduced. sequester RNA using
a eukaryotic RNA regulatory mechanism.
eIF2 forms a complex with GTP. eif2 bind to GTP and its
attracting ribosome to initiator tRNA. small ribosomal subunit
will start to