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A bacterial artificial chromosome (BAC) is a DNA construct, based on a fertility plasmid (or F-plasmid), used for transforming and cloning in bacteria, usually E. coli. F-plasmids play a crucial role because they contain partition genes that promote the even distribution of plasmids after bacterial cell division. The bacterial artificial chromosome's usual insert size is 150 kbp, with a range from 100 to 350 kbp. A similar cloning vector, called a PAC has also been produced from the bacterial P1-plasmid.
BACs are often used to sequence the genetic code of organisms in genome projects, for example the Human Genome Project. A short piece of the organism's DNA is amplified as an insert in BACs, and then sequenced. Finally, the sequenced parts are rearranged in silico, resulting in the genomic sequence of the organism.
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Common gene components
- oriS, repE - F
- for plasmid replication and regulation of copy number.
- parA and parB
- for partitioning F plasmid DNA to daughter cells during division and ensures stable maintenance of the BAC.
- A selectable markers
- for antibiotic resistance, some BACs also have lacZ at the cloning site for blue/white selection.
- T7 & Sp6
- phage promoters for transcription of inserted genes.
Contribution to models of disease
BACs are now being utilised to a greater extent in modeling genetic diseases, often alongside transgenic mice. BACs have been useful in this field as complex genes may have several regulatory sequences upstream of the encoding sequence, including various promoter sequences that will govern a gene's expression level. BACs have been used to some degree of success with mice when studying neurological diseases such as Alzheimer's disease or as in the case of aneuploidy associated with Down syndrome. There have also been instances when they have been used to study specific oncogenes associated with cancers. They are transferred over to these genetic disease models by electroporation/transformation, transfection with a suitable virus or microinjection. BACs can also be utilised to detect genes or large sequences of interest and then used to map them onto the human chromosome using BAC arrays. BACs are preferred for these kind of genetic studies because they accommodate much larger sequences without the risk of rearrangement, and are therefore more stable than other types of cloning vectors.
See also
External links
- The Big Bad BAC: Bacterial Artificial Chromosomes - a review from the Science Creative Quarterly
- Cloning and Stable Maintenance of 300-Kilobase-Pair Fragments of Human DNA in Escherichia coli Using an F-Factor-Based Vector - the initial journal article describing the bacterial artificial chromosome by Shizuya et al.
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