In eukaryotes, what must occur before mRNA exits the nucleus?

In eukaryotic cells, the process of gene expression involves the transcription of DNA into messenger RNA (mRNA) within the nucleus. For this mRNA to become functional and ultimately exit the nucleus, it must undergo several crucial processing steps, which include capping and polyadenylation.

Capping involves the addition of a modified guanine nucleotide to the 5' end of the mRNA molecule. This "cap" protects the mRNA from degradation and is essential for the initiation of translation in the cytoplasm. Polyadenylation occurs at the 3' end of the mRNA, where a tail of adenine nucleotides, known as the poly(A) tail, is added. This tail further protects the mRNA and aids in its stability, transport, and translation efficiency.

These modifications ensure that the mRNA is properly processed, stable, and recognized by the translation machinery once it exits the nucleus. Thus, before mRNA can leave the nucleus and participate in protein synthesis in the cytoplasm, it must indeed undergo capping and polyadenylation.