ExCyto PCR Amplification

ExCyto PCR cells provide a novel and cost effective means to amplify DNA transformed into competent bacterial cells. ExCyto PCR uses host E. coli with a chromosomally integrated gene encoding a thermostable DNA polymerase to accomplish robust, hot-start PCR amplification of cloned sequences without addition of exogenous enzyme.Because the thermostable DNA polymerase is stably integrated into the bacterial chromosome, ExCyto cells can be transformed with a single plasmid or complex library, and then the expressed thermostable DNA polymerase can be used for PCR amplification. We demonstrate that ExCyto cells can be used to amplify DNA from different templates, plasmids with different copy numbers, and master mixes left on ice for up to two hours. Further, PCR amplification with ExCyto cells is comparable to amplification using commercial DNA polymerases. The ability to transform a bacterial strain and use the endogenously expressed protein for PCR has not previously been demonstrated.ExCyto PCR reduces pipetting and greatly increases throughput for screening EST, genomic, BAC, cDNA, or SNP libraries. This technique is also more economical than traditional PCR and thus broadly useful to scientists who utilize analysis of cloned DNAs in their research

Linear plasmid vector for cloning of repetitive or unstable sequences in Escherichia coli

Despite recent advances in sequencing, complete finishing of large genomes and analysis of novel proteins they encode typically require cloning of specific regions. However, many of these fragments are extremely difficult to clone in current vectors. Superhelical stress in circular plasmids can generate secondary structures that are substrates for deletion, particularly in regions that contain numerous tandem or inverted repeats. Common vectors also induce transcription and translation of inserted fragments, which can select against recombinant clones containing open reading frames or repetitive DNA. Conversely, transcription from cloned promoters can interfere with plasmid stability. We have therefore developed a novel Escherichia coli cloning vector (termed ‘pJAZZ’ vector) that is maintained as a linear plasmid. Further, it contains transcriptional terminators on both sides of the cloning site to minimize transcriptional interference between vector and insert. We show that this vector stably maintains a variety of inserts that were unclonable in conventional plasmids. These targets include short nucleotide repeats, such as those of the expanded Fragile X locus, and large AT—rich inserts, such as 20-kb segments of genomic DNA from Pneumocystis, Plasmodium, Oxytricha or Tetrahymena. The pJAZZ vector shows decreased size bias in cloning, allowing more uniform representation of larger fragments in libraries

ExCyto PCR amplification.

<p>A cDNA library was transformed into ExCyto cells. Twenty-four different cDNAs were amplified without addition of exogenous polymerase using (A) single colonies, (B) 2 µl of frozen glycerol stocks, or (C) 2 µl of overnight cultures. One kb molecular weight markers are shown in the last lane.</p

Dilution series of ExCyto PCR cells.

<p>Eight different clones from a cDNA library transformed into ExCyto cells were grown overnight, and a serial dilution was used for amplification (undiluted, 100-, and 1000-fold dilutions). In (A), bacteria were diluted, reducing both the target DNA and the tsDNA polymerase. In (B), to compensate for the serial dilution of the tsDNA polymerase, 2 ul of ExCyto cells (OD 1.1) without plasmids was added. In (C), to compensate for the serial dilution of plasmid, 2 ul of bacteria with the same plasmid, but without the tsDNA polymerase was added. A 10-fold dilution is not shown, but gives similar amplification to that seen with undiluted cells. One kb molecular weight markers are shown in the last lane.</p

ExCyto PCR of chromosomal integrants.

<p>Two µl of overnight cultures from chromosomal integrants were used for PCR with primers flanking the melAmelB bicistron integration site. Integrants show a band at 4.5 kb. Wild type (WT, last lane) has a band at 2 kb. One kb molecular weight markers are shown in the first lane.</p