Imagine that you have engineered a set of genes , each encoding a protein with a pair of conflicting signal sequences that specificy different compartments. If the genes were expressed in a cell, what signal would win and why?
1) A) Signals for import into ER would beat signals for import int the nucleus. What is the reasonable explanation?
1) The nuclear transport receptor is more efficient than the signal recognition particle (SRP)
2) The ER signal near the N-terminus will be exposed before the nuclear signal during protein synthesis and thus recognized by SRP before the nuclear signal is even available
3) the nuclear signal near the middle of the sequence will be exposed before the ER signal during protein synthesis and thus recognized by the nuclear transprot protein before the ER signal is active.
4) the SRP is more efficient than the nuclear transport receptor.
B) Signals for import into ER would beat signals for import into peroxisomes. What is the reasonable explanation?
1) The peroxisome transport proteins are more efficient than the signal recognition particle (SRP)
2) The ER signal near the N-terminus will be exposed before the peroxisome signal during protein synthesis and thus recognized by SRP before the peroxisome signal is even available
3) peroxisome proteins are transported by vesicles not by transport proteins.
4) the SRP is more efficient than the peroxisome transporter.
C) Signals into the mitochondria and retention into the ER? Which would win? Reasonable explanation as to why?
1)Mitochondria
2)ER
and
1) The mitochondrial transport protein is more efficient than the signal recognition particle (SRP)
2) The ER signal near the N-terminus will be exposed before the mitochondrial signal during protein synthesis and thus recognized by SRP before the mitochondrial signal is even available
3) the mitochondrial signal near the N-terminus of the sequence will be exposed before the ER retention during protein synthesis and thus recognized by the SRP before the ER signal is active
4) the signal for retention of a protein in the ER is at the C-terminus and not recognized until import into the ER begins
