BIOL 413 TAMU Farhy Chap 7 Gene Control

Mechanisms to control cell types

Maintenance methyl transferase

methylation

DNA methylation

adds to cytosine, stops transcription
removed by demethylases

Maintenance methyl transferase

adds methyl group to C, allows pattern to be inherited after replication
indiscriminate

Post transcriptional control

transcription attenuation
riboswitches
alt. splicing/polyadenylation site
covalent modification
regulation of nuclear transport
compartmentalization

Transcription attenuation + example

premature termination of transcription by RNA polymerase
Ex: HIV removing proteins that would normally cause attenuation to stop viral genome from reproducing

Riboswitch + example

short RNA sequence that blocks transcription when bound to reg molecule
Ex: purine synthesis, on when bound

alt. splicing

removing introns and exons
neg reg - reg molecule stops from accessing site, pos reg opposite

alt splicing and polyadenylation site + example

selective cut in C-terminal to change protein, affects splicing if in intron
ex: B lymphocytes

covalent modification + example

func group removed or added to RNA nucleotides that generates diff nucleotide
methyladenosine-methylated adenine by methylase enzymes
transient mod - removed by demethylases

Ex: apolioprotein B, edits proteins in liver and intestine so one in intestine is shorter to make diff protein

regulation of nuclear transport + example

mRNA must be spliced before sent out
Ex: HIV must overcome block with REV to send out non spliced RNA for transport

Compartmentalization

RNA localization allows concentration of specific RNAs in compartments for asymmetry
allows cell to independently control translation in diff compartments

Mechanisms controling translation initiation

shine dalgarno seq
temp control
riboswitch
microRNA
elF2
internal ribosome entry site (IRES)

shine dalgarno seq

site of repressor or promoter for translation

temp control

can change mRNA structure and expose AUG

riboswitch

can expose AUG (allowing translation)

mRNA binding

mRNA binds to RNA to promote degradation and reduce protein levels

elF2 & elF2B

elF2 = translation initiation factor, triggers translation when bound to GTP, turns to GDP when seeing AUG
elF2B promotes GDP-GTP exchange to reuse elF2
Phosphorylation of elF2 - prevents GDP exchange
depleting elF2 GTP slows translation

Internal ribosome entry site (IRES) + example

mRNA seqs that allow initiation in 2 locations, ensures separate translation
Ex: viruses produce protease that shuts down elF2 host translation and causes translation of its IRES

RNA stability factors

poly-A shortening
P-bodies
stress granule