Infection of Ecoli Cells with Lambda Vectors - The A vectors can be used as naked DNA to transform E. coli cells, or they may be packaged into phage particles and used to infect the host cells; plaque formation by the latter is 100-10,000 times of that obtained by the former.

In vitro packaging of A vectors is achieved by mixing the concatameric form of vector with preformed empty phage heads, tails and terminase.

Terminase specifically binds close to the cas sites; it cleaves the cas sites to generate the typical cohesive ends of the A genome. Special techniques and A mutants are required for the preparation of empty heads, tails and DNA-free terminase.