Bacterial artificial chromosomes

Existing vectors

BAC vectors

• F-factor plasmid based vectors
• original BAC vectors are 7.4 kb, others are 8-9kb.
• can clone 80-300kb fragments, sometimes more
• usually the host need to be deficient in homologous recombination machinery in order for the BAC to be stable (i.e. recA^-). Usually DH10B is used as the host.
• can retrofit BAC vectors with a particular insert by using a retrofitting vector like pRetroES (Ref 3)

pBAC108L

• no selection system for inserts
• one of the original vectors

pBeloBAC11

• recommended by Tom, have this in the lab
• screen for inserts via α-complementation (blue-white screening on IPTG/Xgal plates)
• does not have a selection marker for transfection into mammalian cells
• pBeloBAC11 from NEB

pBACe3.6

• transferred the pUC-link and SacBII sequences from a PAC vector to pBAC108L. See below.
• does not have a selection marker for transfection into mammalian cells

pFos1

• pFos1 from NEB
• "Grow cells at 30°C. The plasmid is unstable at 37°C."
• "The plasmid pFOS1 carries a gene encoding resistance to ampicillin (amp) and a gene encoding resistance to chloramphenicol (cam). To maintain the plasmid, cells should be grown with 100 µg/ml amp and 15-20 µg/ml cam."

pFW11 and F' factor

• from Ref 1
• available through Natalie from an HMS lab
• clone insert into pFW11 between 3' end of lacI and 5' end of lacZ. Transferred via homologous recombination to the complete lac operon (lacZYA) on the F' episome. Then F' moves to another strain via conjugation which is distinguished from the original strain by streptomycin resistance.
• distinguish between single recombinants (both episomes) and double recombinant F' via the marker sensitivity.
• method designed to test DNA binding proteins and cognate promoters via β-galatosidase activity.
• pFW11 has a strong terminator upstream of the polylinker
• may be a more sophisticated system than we need?

SuperCos 1

• SuperCos 1 from Stratagene
• we have it?
• Tom says we got it from Epicentre
• "Cosmid vectors are valuable tools in this analysis, because they can accommodate genomic DNA fragments ranging in size from 30 to 42 kb."
• "SuperCos 1 is a novel, 7.9-kb cosmid vector that contains bacteriophage promoter sequences flanking a unique cloning site."
• "The SuperCos 1 vector is also engineered to contain genes for the amplification and expression of cosmid clones in eukaryotic cells."
• "Most genomic inserts can be excised as a single large restriction fragment using the Not I restriction site that flanks the SuperCos 1 polylinker."
• cos sites are for in vitro packaging with λ
• has a pUC origin on the map. Is this eliminated in the λ packaging step?

pCC1BAC

• CopyControl pCC1BAC vector from Epicentre
• "contains the E. coli F-factor single-copy origin of replication and an inducible high-copy oriV origin of replication."
• "grown at single-copy number to ensure insert stability. Then, clones can be induced to 10-20 copies per cell within 2 hours of adding CopyControl Induction Solution to the culture, for higher yields and higher purity DNA. Although large-insert clones are less stable when cloned and maintained in high-copy vectors, the short 2-hour induction of CopyControl BAC clones to high-copy-number does not decrease their stability, based on analysis of Hind III restriction patterns of a large number of induced versus uninduced clones that ranged in size up to ~200 kb."

pIndigoBAC-5

• pIndigoBAC-5 from Epicentre
• "derived from pBeloBAC11 and pIndigoBAC1 and will accommodate and stably maintain DNA inserts of >100 kb." *"linearized at its unique BamH I or Hind III site, dephosphorylated, and highly purified and is ready for cloning BamH I- or Hind III-cut genomic DNA. The linearized and dephosphorylated vectors are tested to ensure the completeness of linearization, dephosphorylation, and the integrity of the BamH I and Hind III ends."
• "The complete sequence and restriction map of pIndigoBAC-5 is available."
• "Enhanced blue/white screening of recombinants."

PAC vectors

• derived from bacteriophage P1 vector
• 15-16kb
• positive selection for inserts via sacB the levansucrase gene which converts sucrose to levan which is toxic to E. coli
• a pUC-vector-derived fragment is inserted into the cloning site which inactivates sacB and allows large amounts of vector to be purified. Your insert replaces this pUC vector thereby returning the vector to single copy. Must be careful to ensure that no uncut vector is present in cloning because it will transform as well as the insert containing vectors. Thus, the sacB marker only prevents against vector religation productions not intact vector.

Protocol notes

BAC purification

• exist as supercoiled circular plasmids and are resistant to shearing making purification easier
• most purification protocols appear to be geared for preparation of genomic libraries for sequencing. It is not clear if we need such elaborate protocols for simple clonings.
• Typical DNA yields
  1. 1μg from 5mL LB culture sing alkaline BAC DNA purification
  2. 0.8μg from 1.3mL TB culture using Qiagen R.E.A.L.
  3. 4μg from 20mL LB culture using Qiagen-tip 20
  4. 100μg from 500mL LB culture using Qiagen-tip 500

Putting the BAC into E. coli

1. Transformation
   • has low efficiencies
   • works on any size
2. In vitro packaging
   • package the vector inside λ bacteriophage particles and infect cells
   • limits the size of the DNA because of phage head stability. The phage head is not stable if the vector is too small or too large. Usually ~40kb insert with an 8-9kb vector works.

References

1. F. W. Whipple. Genetic analysis of prokaryotic and eukaryotic dna-binding proteins in escherichia coli. Nucleic Acids Res, 26(0305-1048):3700–6, 1998.
2. Bacterial artificial chromosomes. S. Zhao and M. Stodolsky, editors, Volume 1: Library Construction, Physical Mapping, and Sequencing, volume 255 of Methods in Molecular Biology. Humana Press, 2004.
3. Bacterial artificial chromosomes. S. Zhao and M. Stodolsky, editors, Volume 2: Functional Studies, volume 256 of Methods in Molecular Biology. Humana Press, 2004.
4. Evans, G. A., Lewis, K. and Rothenberg, B. E. (1989). High efficiency vectors for cosmid microcloning and genomic analysis. Gene 79: 9-20.
5. Hohn, B. and Collins, J. (1980). A small cosmid for efficient cloning of large DNA fragments. Gene 11: 291-298.