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Types of artificial chromosomes

BAC – Bacterial artificial chromosome

This is another popular artificial chromosome used in genetic engineering. The main difference between it and the yeast artificial chromosome is that YAC can contain up to three times more DNA, but the BAC is more stable.

This characteristic makes it the preferable choice when doing some genetic experiments like sequencing; especially since bacterial artificial chromosome can still contain a lot of DNA, up to around 300 kb), which is a lot more than regular plasmids or virus-based vectors. It was used during the genome projects, like in the case of Human Genome Project, which was started with YAC, but scientists decided to shift to BAC after the yeast artificial chromosome proved to be unstable. The basic idea behind the genome project is to have the organism’s whole sequence. This can be accomplished by sequencing the organism’s genome – amplifying it using BAC vectors (containing inserts of organism’s DNA) and PCR. The final sequence is ordered and produced using computers.

Bacterial artificial chromosome is based on the F-plasmid (fertility plasmid). This is important since F-plasmid contains parA and parB partition genes which contribute to the overall stability of the BAC, plus they partition the vector DNA to daughter cells during the cell division, resulting in even distribution of plasmid after the division.

Additional parts of the bacterial artificial chromosome are selectable markers, of course, like the ones for antibiotic resistance or blue/white selection. Also repE region, which is responsible for the replication initiator protein whose role is also to regulate the number of copies of BAC. It also contains the target sites where restriction enzymes will cut and where the DNA of interest will be inserted, and it has T7 and Sp6 regions, which are phage promoters, sites of the RNA pol binding and the initiation of transcription (RNA production).