• Homopolymer Tailing in Recombinant DNA Technology:
• Terminal Deoxynucleotidyl Transferase (TdT): A template-independent DNA polymerase that adds successive deoxynucleotides to the $3'\text{-OH}$ end of DNA.
• When supplied with a single dNTP (e.g., dGTP or dCTP), TdT synthesizes a continuous homopolymeric tail (e.g., poly-dG on vector and poly-dC on insert cDNA), allowing complementary annealing and cohesive cloning without restriction enzyme cleavage.
• nalysis:
• (Terminal deoxynucleotidyltransferase): Correct enzyme.

Correct option: (2) Terminal deoxynucleotidyltransferase

• DNA Ligase Function: DNA ligases catalyze the formation of a covalent phosphodiester bond between adjacent $3'\text{-OH}$ and $5'\text{-phosphate}$ termini of nicked double-stranded DNA.
• Biological Role: Essential for joining Okazaki fragments on the lagging strand during DNA replication, as well as sealing repaired nicks during excision repair and recombination.
• Energy Requirement: Eukaryotic and bacteriophage T4 ligases require ATP, while bacterial DNA ligases (e.g., E. coli) utilize $\text{NAD}^+$ as a cofactor.

Correct option: (2) Phosphodiester bonds between nucleotides.