Bacterial artificial chromosome explained

A bacterial artificial chromosome (BAC) is a DNA construct, based on a functional fertility plasmid (or F-plasmid), used for transforming and cloning in bacteria, usually E. coli.[1] [2] [3] 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 150–350 kbp.[4] A similar cloning vector called a PAC has also been produced from the DNA of P1 bacteriophage.

BACs were often used to sequence the genomes of organisms in genome projects, for example the Human Genome Project, though they have been replaced by more modern technologies. In BAC sequencing, 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. BACs were replaced with faster and less laborious sequencing methods like whole genome shotgun sequencing and now more recently next-gen sequencing.

Common gene components

repE: 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 marker: 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

    Inherited disease

    BACs are now being utilized to a greater extent in modelling 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 utilized 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.

    Infectious disease

    The genomes of several large DNA viruses and RNA viruses have been cloned as BACs. These constructs are referred to as "infectious clones", as transfection of the BAC construct into host cells is sufficient to initiate viral infection. The infectious property of these BACs has made the study of many viruses such as the herpesviruses, poxviruses and coronaviruses more accessible.[5] [6] [7] Molecular studies of these viruses can now be achieved using genetic approaches to mutate the BAC while it resides in bacteria. Such genetic approaches rely on either linear or circular targeting vectors to carry out homologous recombination.[8]

    See also

    External links

    Notes and References

    1. O'Connor M, Peifer M, Bender W . Construction of large DNA segments in Escherichia coli . Science . 244 . 4910 . 1307–12 . June 1989 . 2660262 . 10.1126/science.2660262 . 1989Sci...244.1307O .
    2. Shizuya H, Birren B, Kim UJ, Mancino V, Slepak T, Tachiiri Y, Simon M . Cloning and stable maintenance of 300-kilobase-pair fragments of human DNA in Escherichia coli using an F-factor-based vector . Proceedings of the National Academy of Sciences of the United States of America . 89 . 18 . 8794–7 . September 1992 . 1528894 . 50007 . 10.1073/pnas.89.18.8794 . 1992PNAS...89.8794S . free .
    3. Shizuya H, Kouros-Mehr H . The development and applications of the bacterial artificial chromosome cloning system . The Keio Journal of Medicine . 50 . 1 . 26–30 . March 2001 . 11296661 . 10.2302/kjm.50.26 . free .
    4. Stone NE, Fan JB, Willour V, Pennacchio LA, Warrington JA, Hu A, de la Chapelle A, Lehesjoki AE, Cox DR, Myers RM . Construction of a 750-kb bacterial clone contig and restriction map in the region of human chromosome 21 containing the progressive myoclonus epilepsy gene . Genome Research . 6 . 3 . 218–25 . March 1996 . 8963899 . 10.1101/gr.6.3.218 . free .
    5. Almazán F, González JM, Pénzes Z, Izeta A, Calvo E, Plana-Durán J, Enjuanes L . Engineering the largest RNA virus genome as an infectious bacterial artificial chromosome . Proceedings of the National Academy of Sciences of the United States of America . 97 . 10 . 5516–21 . May 2000 . 10805807 . 25860 . 10.1073/pnas.97.10.5516 . free .
    6. Domi A, Moss B . Cloning the vaccinia virus genome as a bacterial artificial chromosome in Escherichia coli and recovery of infectious virus in mammalian cells . Proceedings of the National Academy of Sciences of the United States of America . 99 . 19 . 12415–20 . September 2002 . 12196634 . 129459 . 10.1073/pnas.192420599 . 2002PNAS...9912415D . free .
    7. Messerle M, Crnkovic I, Hammerschmidt W, Ziegler H, Koszinowski UH . Cloning and mutagenesis of a herpesvirus genome as an infectious bacterial artificial chromosome . Proceedings of the National Academy of Sciences of the United States of America . 94 . 26 . 14759–63 . December 1997 . 9405686 . 25110 . 10.1073/pnas.94.26.14759 . 1997PNAS...9414759M . free .
    8. Feederle R, Bartlett EJ, Delecluse HJ . Epstein-Barr virus genetics: talking about the BAC generation . Herpesviridae . 1 . 1 . 6 . December 2010 . 21429237 . 3063228 . 10.1186/2042-4280-1-6 . free .

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