Regulation of Translation: Molecular Biology

Final

What is the most general and nonspecific way of regulating translation?

controlling the ribosome number in the cell

How is the ribosome number regulated in bacteria?

synthesis and degradation, especially degradation of the 30S and 50S subunits

What is the major mechanism that some bacteria (e.g. E. coli) use to coordinate
production of rRNA and r-proteins?

genes for most of r-proteins are clustered, and their synthesis is regulated by autogenous feedback

What is the most rapid and specific way to regulate translation?

through control of translation initiation

What does control of translation initiation in eukaryotes involve?

binding of factors to the cap sequence (via cap binding proteins), internal ribosome entry sites (IRES), or the 3’-UTR

What is the protein factor that is required for the cap-dependent initiation?

elF4F

What are the major components of the eIF4F and their respective functions?

elF4E—cap binding, eIF4A—helicase, eIF4G—scaffolding, interacting with both eIF4E and PABP

Why is involvement of PABP in translation initiation important?

ABP connects the poly(A) tail with the 5’-end to circularize the mRNA, which enhances translation efficiency

When is IRES used to initiate translation?

used when normal cap-dependent initiation is impaired

What are riboswitches?

secondary structural elements in some mRNA that change their conformation in response to some external stimulus, such as temperature, binding of a metabolite, thereby turn on or off the translation of that mRNA

how do miRNAs affect translation or degradation of mRNA?

miRNAs bind to 3’-UTR, recruitment of AGO to form miRISC, leading to destruction of mRNAs or repression of translation

What are the major components of miRISC?

AGO, protein GW182, PABP

What is the contribution of mRNA stability to the control of translation?

It plays a major role in determining the protein levels in the cell

What are the two major pathways of decay for nonfaulty mRNAs?

Decapping followed
by 5’ to 3’ decay, 3’ to 5’ decay and decapping; both pathways start with deadenylation

What are the major factors involved in mRNA decapping?

Dcp2 and factors that positively (e.g. Dcp1, LSm1-7) or negatively (e.g. PABP, VCX-A) regulate its activity

What is the major content of the P body?

mRNAs, exonuclease Xrn1, deadenylation complex, decapping complex

What is the major content of the stress granules?

mRNA, small ribosomal subunit, translation initiation factors

Faulty mRNAs are degraded by

nonsense-mediated decay (premature stop codon), no-go decay (ribosome stalling), or non-stop decay (missing stop codon)