MolBio11 - 26 Flashcards
What are isoforms?
The different forms of protein that can be made from a single gene
How are isoforms created?
Alternate splice sites, start sites, poly-A sites
Where are isoforms most important for humans?
Immune system - generation of a/b from very small number of genes
Where is the most dramatic array of isoforms?
Neural - 38,000
What is the best characterised form of the regulation of alternative splicing?
Sex determination in drosophila - female have two Xs, males have one
What three genes regulate male and female differentiation in drosophila?
Sex lethal (sxl), transformer (tra), doublesex (dsx)
What is different in male drosophila splicing than in female?
sxl and tra are spliced to give rise to inactive proteins, resulting in a large dsx splice
What do dsx transcripts give rise to?
Either female or male repressive proteins, dependent on splicing
Outline the female drosophila sxl/tra/dsx pathway
Splice site in sxl blocked = functional sxl, sxl upregulates itself and blocks tra = functional tra, tra increases dsx splice length = repressor of male differentiation genes
Where does sxl bind?
U2AF
Which cell type exhibits polyA splice site isoforms?
B lymphocytes
What are the two B lymphocytic splices?
Long transcript = first stop spliced out = translation of a transmembrane domain; short transcript = splice lost = stop not lost = antibody secretion
What is the optimual start sequence?
Kozak sequence - accAUGg
How are alternative start sites identified?
Leaky scanning - small ribosome scans past first and stops and second or third
What favours the first AUG in a cell?
High levels of eIF-4F
