The RNA species that carries the coded message specifying the sequence of amino acids in a protein from the nucleus to the cytoplasm is messenger RNA (mRNA).

Here's why:

* DNA contains the genetic code: DNA holds the instructions for building proteins, but it remains safely stored within the nucleus.

* Transcription: mRNA is created in the nucleus through a process called transcription. This involves copying the DNA code for a specific gene into an mRNA molecule.

* Translation: The mRNA molecule then travels out of the nucleus and into the cytoplasm, where it interacts with ribosomes. Ribosomes read the mRNA code in groups of three nucleotides called codons. Each codon corresponds to a specific amino acid.

* Protein Synthesis: The ribosome uses the information from the mRNA to assemble amino acids in the correct order, creating the polypeptide chain that will eventually fold into a functional protein.

So, mRNA acts as the messenger, carrying the genetic instructions from the nucleus to the cytoplasm, where proteins are made.