Final answer:
Messenger RNA (mRNA) leaves the nucleus through nuclear pores aided by modifications like the 5' cap and poly(A) tail, which are recognized by proteins that guide the mRNA out to the cytoplasm for translation.
Step-by-step explanation:
mRNA exits the nucleus of a cell through structures known as nuclear pores. Inside the nucleus, mRNA is processed and collects a 5' methylguanosine cap and a poly(A) tail. These modifications are recognized by nuclear transport receptors and associated proteins, which guide the mRNA through the nuclear pores into the cytoplasm, where ribosomes then use the mRNA template for protein synthesis.