Posttranscriptional Regulation in Eukaryotes

Flashcards related to posttranscriptional regulation in eukaryotes. Including topics of alternative splicing, mRNA stability/ degradation, mRNA localization and posttranslational modifications.

Posttranscriptional Regulation

Changes made to pre-mRNA during their conversion to mature mRNA. Each step can be regulated to control gene expression.

RNA Splicing

The removal of noncoding introns from a pre-mRNA to form a mature mRNA.

Alternative Splicing

A process where pre-mRNA can be spliced in different ways, generating different spliceforms (or isoforms) of the same gene, leading to proteins with different amino acids and functions.

Cassette Exons

Exons that may be excluded in the mature mRNA; common in animals, where the spliceoforms have the same terminal 3' end.

Alternative Splice Site

Located within an exon that may be upstream or downstream of the normally used splice site.

Intron Retention

Introns, which are normally noncoding sequences, are included in the mature mRNA and are translated; common in plants, fungi, and protozoa.

Mutually Exclusive Exons

The swapping of protein domains encoded by different exons, where the inclusion of one exon leads to the exclusion of the others in the same cluster of adjacent exons.

Alternative Promoters

Having more than one site where transcription may be initiated, producing pre-mRNAs with different 5' exons.

Alternative Polyadenylation

Producing isoforms with different 3' ends, where the poly-A tail signals termination of transcription, hence downstream exons are omitted.

mRNA Stability and Degradation

RNA is susceptible to degradation (decay) which stops translation. Regulates gene expression and alters the amount of mRNA available for translation.

Exoribonuclease

Enzymes that degrade RNA via removal of terminal nucleotides.

Deadenylation-dependent decay

Shortening of the length of 3’ poly-A tail by exoribonuclease/deadenylase. If shortened to <30 nt, the mRNA will be degraded

Processing (P) bodies

Cytoplasmic structures containing decapping enzymes and exoribonucleases; localized centers for mRNA decay.

mRNA surveillance through non-sense mediated decay (NMD)

Eliminates mRNA with premature stop codons (caused by nonsense mutation), leading to truncated and nonfunctional protein.

Cytoplasmic Polyadenylation

Controls translation initiation and regulation of 3’ poly-A tail.

Localized Translation

Some mRNAs are localized to discrete regions within the cell to produce protein only when and where it is needed.

Zip Code

A 54-nt sequence in the actin mRNA 3’ UTR that is the binding site for zip code binding protein 1 (ZBP1).

ZBP1

A protein that binds to the zip code in the actin mRNA 3’ UTR, blocking translation until mRNA is localized to the site of the cell where it is needed.

Posttranslational Modifications

Changes that can alter a protein’s stability, subcellular localization, affinity for other proteins/nucleic acids/molecules; enzyme-catalyzed via covalent attachment of molecules.

Phosphorylation

The addition of a phosphate group to serine, tyrosine, or threonine amino acids via kinase; induces conformational changes and functional changes in proteins.

Ubiquitination

Covalent attachment of 76-aa ubiquitin to target protein via a lysine side chain; ubiquitin chains act as tags that mark the protein for degradation.