Allison P. Null

Advantages of thermococcus kodakaraenis (KOD) DNA Polymerase for PCR-mass spectrometry based analyses

The advantages of the thermostable DNA polymerase from Thermococcus kodakaraensis (KOD) are demonstrated for PCR amplification with subsequent detection by mass spectrometry. Commonly used DNA polymerases for PCR amplification include those from Thermus aquaticus (Taq) and Pyrococcus furiosus (Pfu). A 116 base-pair PCR product derived from a vWA locus was amplified by Taq, Pfu, or KOD DNA polymerase and compared by agarose gel electrophoresis and electrospray ionization Fourier transform ion cyclotron resonance mass spectrometry (ESI-FTICR-MS). KOD DNA polymerase demonstrated a 2- to 3-fold increase in PCR product formation compared to Pfu or Taq, respectively, and generated blunt-ended PCR product which allows facile interpretation of the mass spectrum. Additionally, we demonstrate the advantage of using high magnetic fields to obtain unit resolution of the same 116 base pair (∼72 kDa) PCR product at high m/z.

Evaluation of sample preparation techniques for mass measurements of PCR products using ESI-FT-ICR mass spectrometry

Elimination of PCR buffer components and alkali metal cations (i.e., Na+, K+) is of critical importance to allow for accurate mass measurements of PCR products for genotyping and sequencing applications. Ethanol precipitation followed by microdialysis has been repeatedly shown to efficiently desalt PCR products for analysis by mass spectrometry and is considered the gold standard. Alternative cleanup techniques that are compatible with automation are explored here with the intent of expanding the bottleneck that exists between the production of PCR products and analysis by electrospray ionization mass spectrometry (ESI-MS). Numerous combinations of approaches were evaluated that included PCR purification kits and alcohol precipitations. The data shown here support alternative approaches to an ethanol precipitation followed by microdialysis that have comparable desalting efficiency and can be utilized for cleanup of PCR products generated from single reactions.

Genotyping complex short tandem repeats using electrospray ionization Fourier transform ion cyclotron resonance multistage mass spectrometry

Electrospray ionization Fourier transform ion cyclotron resonance (ESI-FTICR) mass spectrometry is a rapidly emerging, universal platform with the ability to provide detailed information regarding genetic variation and the up- and down regulation of their cognate gene products. Herein, we report our progress towards the development of ESI-FTICR mass spectrometry for the characterization of genomic regions which contain both a length and sequence polymorphism (i.e., complex short tandem repeats). Specifically, it is demonstrated for the first time that a high-quality ESI-FTICR mass spectrum of a 82-bp double- stranded PCR product derived from a single, 50 (mu) L PCR reaction with less than 10 X 10-15 moles injected into the mass spectrometer can be routinely obtained. It is important to note that each measurement, which translates to an accurate genotype, is completed on the timescale of seconds. Progress towards the implementation of flow- injection analysis methodology to increase the throughput is also presented using an alternating injection of a 15-mer and 16-mer oligonucleotide.

CEPH family 1362 STR database: An online resource for characterization of PCR products using electrospray ionization mass spectrometry

An online database has been established in order to validate electrospray ionization mass spectrometry (ESI-MS) for genotyping and to publicize the procedures developed in our laboratory for the characterization of PCR products by ESI-MS. Genotypes derived from short tandem repeat (STR) loci that were obtained using ESI Fourier transform ion cyclotron resonance mass spectrometry (FTICR-MS) have been posted for fifteen members of the CEPH family 1362 pedigree. The website provides specific information such as PCR parameters, PCR product cleanup approaches, and ESI solution compositions to enable other laboratories to reproduce our data. Links are provided to related websites in an effort to integrate information regarding the CEPH family, STR genotyping, and mass spectrometry. The database, currently available at http://www.people.vcu.edu/~dcmuddim/genotype/ will be routinely updated with genotypes from additional STR loci including PCR parameters as well as PCR cleanup strategies as further developments are completed.