• Mechanism of $\alpha$-Complementation:
• The host E. coli strain (e.g., DH5$\alpha$, JM109) carries a mutant $\beta$-galactosidase gene (lacZ$\Delta M15$) encoding an inactive enzyme missing its N-terminal segment (the $\alpha$-peptide).
• The plasmid vector (e.g., pUC19, pBluescript) carries the coding sequence for this missing $\alpha$-peptide within its multiple cloning site (MCS).
• In transformed cells, the plasmid-encoded $\alpha$-peptide physically complexes with the host's inactive dimer to reconstitute functional $\beta$-galactosidase holoenzyme by providing the missing N-terminal domain.
• Functional enzyme cleaves chromogenic X-gal to produce blue colonies; insertion of foreign DNA disrupts the $\alpha$-peptide, yielding white recombinant colonies.
• nalysis:
• (alpha; beta-galactosidase; N-terminal): Correct.

Correct option: (2) alpha; beta-galactosidase; N-terminal