Which of the following are the post-transcriptional events in an eukaryotic cell?

A. Transport of pre-mRNA to cytoplasm prior to splicing.
B.Removal of introns and joining of exons.

C.Addition of methyl group at 5’ end of hnRNA.

D.Addition of adenine residues at 3' end of hnRNA.

E.Base pairing of two complementary RNAs.

Choose the correct answer from the options given below :

The correct answer is B, C, D only.

Post‑transcriptional events are modifications that occur to the primary RNA transcript **after** it has been synthesized by RNA polymerase but **before** it becomes a functional messenger RNA (mRNA) in the cytoplasm. These events typically take place in the nucleus and include splicing, capping, and polyadenylation.

Option B: Removal of introns and joining of exons is the classic splicing reaction. It trims the pre‑mRNA by excising non‑coding introns and ligating the remaining exons, converting the transcript into a mature mRNA. This clearly occurs after transcription.

Option C: Addition of a methyl group at the 5’ end of hnRNA (the 5’ cap) protects the RNA from degradation, assists in ribosome binding, and is added co‑transcriptionally but is considered a post‑transcriptional modification because it occurs after the nascent RNA chain is formed.

Option D: Addition of adenine residues at the 3’ end of hnRNA (poly‑A tail) is the polyadenylation process. It enhances mRNA stability and export, and it is a hallmark post‑transcriptional modification.

Option A: Transport of pre‑mRNA to the cytoplasm prior to splicing would require the RNA to leave the nucleus before it is processed. In eukaryotes, splicing (removal of introns) normally occurs **in the nucleus** before export, so this is **not** a post‑transcriptional event.

Option E: Base pairing of two complementary RNAs describes an interaction such as RNA‑RNA hybridization (e.g., siRNA binding). This is a functional activity of RNA molecules, not a processing step that modifies the pre‑mRNA after transcription.

Therefore, the only statements that correctly describe post‑transcriptional events are B, C, and D.