What is the Poly A tail added to during RNA processing?

The addition of the Poly A tail occurs during the processing of precursor messenger RNA (pre-mRNA) to form mature messenger RNA (mRNA) in eukaryotic cells. This polyadenylation process involves adding a series of adenine nucleotides to the 3' end of the mRNA molecule after transcription. The poly A tail serves multiple important functions; it enhances the stability of the mRNA, facilitates its export from the nucleus to the cytoplasm, and promotes translation into protein.

While rRNA and tRNA are also essential RNA molecules involved in protein synthesis, they do not undergo polyadenylation. Instead, rRNA is a key component of ribosomes and is processed differently within the nucleolus, and tRNA molecules are processed in ways specific to their role in translating the genetic code. DNA, on the other hand, is the template for RNA synthesis and does not have a Poly A tail. Therefore, the correct association of the Poly A tail is specifically with mRNA during its post-transcriptional modification.