Bacterial Artificial Chromosomes

Bacterial artificial chromosomes (BACs) are circular DNA molecules. They con­tain a replicon that is based on the F factor comprising oriS and repE encoding an ATP-driven helicase along with parA, parB, and parC to facilitate accurate partition­ing (see Part 1). The F factor is capable of carrying up to one quarter of the E. coli chromosome and, thus, BACs are capable of maintaining very large DNA inserts (often up to 350 kb); however, many BAC libraries contain inserts of around 120 kb. Newer versions of BAC vectors contain sites to facilitate recovery of cloned DNA (e.g., loxP) (7). A DNA fragment is cloned into BAC vectors in a similar fashion to cloning into general cloning vectors; DNA is ligated to a linearized vector and then introduced into an E. coli cloning strain by electroporation.