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 :

In eukaryotic cells, the primary RNA transcript (hnRNA) undergoes several modifications after transcription before it becomes a mature messenger RNA (mRNA). These modifications are called post‑transcriptional events.

**B. Removal of introns and joining of exons** – This process is known as RNA splicing. Introns are non‑coding sequences that must be excised, and the remaining exons are ligated together to form a continuous coding region. Splicing occurs in the nucleus after transcription.

**C. Addition of a methyl group at the 5’ end of hnRNA** – This refers to the formation of the 5’ cap. A 7‑methylguanosine cap is added to the 5’ terminus of the nascent transcript, protecting it from degradation and facilitating ribosome binding during translation.

**D. Addition of adenine residues at the 3’ end of hnRNA** – This describes polyadenylation. A stretch of adenine nucleotides (the poly‑A tail) is added to the 3’ end, which also enhances mRNA stability and aids in nuclear export.

**Why the other options are not post‑transcriptional events:**

• **A. Transport of pre‑mRNA to the cytoplasm prior to splicing** – In eukaryotes, splicing generally occurs in the nucleus before the mRNA is exported; therefore, export before splicing is not a typical post‑transcriptional modification.

• **E. Base pairing of two complementary RNAs** – This describes hybridization or RNA‑RNA interactions, not a processing step that modifies the primary transcript.

Consequently, the correct set of post‑transcriptional events is **B, C, D only**.