How does TA cloning work and what are its applications?

TA cloning exploits the terminal transferase activity of Taq polymerase, which adds a single adenine to 3' ends of PCR products. TA vectors are linearized with single thymine overhangs that base-pair with the A-overhangs on PCR products, enabling direct ligation without restriction digestion. Commercial vectors (pGEM-T, TOPO-TA) are pre-linearized with T-overhangs. TOPO vectors additionally have topoisomerase covalently bound, enabling 5-minute ligation without ligase. Applications include rapid cloning of PCR products for sequencing, subcloning, and library construction. Limitations include inability to use high-fidelity polymerases (which produce blunt ends) without A-tailing treatment.