Here's why:

* mRNA carries genetic information: It's a copy of a gene's DNA sequence, carrying instructions for building a specific protein.

* Transcription in the nucleus: DNA is transcribed into mRNA inside the nucleus.

* Export for protein synthesis: The mRNA molecule leaves the nucleus through nuclear pores and travels to the cytoplasm, where ribosomes translate it into a protein.

Other molecules exported from the nucleus include:

* tRNA (transfer RNA): Carries amino acids to ribosomes for protein synthesis.

* rRNA (ribosomal RNA): A component of ribosomes.

* snRNA (small nuclear RNA): Involved in splicing and other processes within the nucleus.

Let me know if you'd like to know more about any of these molecules!