For multi$-$pass transmembrane proteins to be correctly inserted into the ER

membrane, what is required?

A$.$ A signal sequence at the N$-$terminus and then pairs of start$-$stop signal sequences

for each transmembrane domain.

B$.$ A signal sequence at the C$-$terminus and then pairs of start$-$stop signal sequences

for each transmembrane domain.

C$.$ An internal signal sequence and then pairs of stop$-$start signal sequences for each

cytosolic loop.

D$.$ An internal signal sequence and then pairs of stop$-$start signal sequences for each

ER lumen loop.

E$.$ None of the above