pRNA is the product of chemically linked amino acids.
Explanation:
All the other choices are exactly the roles of RNA in protein synthesis: mRNA "messenger" RNA transcribes the DNA and travels out of the nucleus; then rRNA "ribosomal" RNA in the ribosome helps assemble the protein using the mRNA; tRNA "transfer" RNA brings amino acids to the assembly line of ribosome and mRNA.
There is no pRNA that I know of, although there are many types of other RNAs like piRNAs (piwi RNAs!) or siRNAs.
