Comparative genomics, analyzing variation among individual genomes, is an area of intense investigation. DNA sequencing is usually employed to look for polymorphisms and mutations. Pyrosequencing, a real-time DNA sequencing method, is emerging as a popular platform for comparative genomics. Here we review the use of this technology for mutation scanning, polymorphism discovery and chemical haplotyping. We describe the methodology and accuracy of this technique and discuss how to reduce the cost for large-scale analysis. Copyright # 2002 John Wiley & Sons, Ltd.Keywords: SNP; Pyrosequencing; re-sequencing; bioluminescence; haplotyping; mutation detection; luciferase Determination of mutations and polymorphisms in a genome is one of the most important tasks in the studies of biological systems today. Three DNA sequencing platforms are now being used to scan for mutations and polymorphisms. These include Sanger DNA sequencing [22] hybridizationbased sequencing [4,6,10,23,24] and Pyrosequencing [17,20]. Pyrosequencing is based on the detection of released pyrophosphate (PPi) during DNA synthesis. In a cascade of enzymatic reactions, visible light proportional to the number of incorporated nucleotides is generated (Figure 1). The cascade starts with a nucleic acid polymerization reaction in which inorganic pyrophosphate (PPi) is released as a result of nucleotide incorporation by polymerase. The released PPi is subsequently converted to ATP by ATP sulfurylase which provides the energy to luciferase to oxidize luciferin and generate light. Since the added nucleotide is known, the sequence of the template can be determined (Figure 1). Pyrosequencing has the potential advantages of accuracy, flexibility, parallel processing and can be easily automated. Furthermore it dispenses with the need for labelled primers, labelled nucleotides and gel-electrophoresis [21]. The methodological performance of Pyrosequencng in determination of difficult secondary DNA Current Pyrosequencing strategy using a commercial machine allows more than 50 nucleotides to be de novo sequenced routinely. Pyrosequencing may be the method of choice for sequencing of difficult secondary DNA structures which cannot be sequenced by conventional sequencing. In this review we discuss the use of Pyrosequencing for mutation scanning, SNP scanning and haplotyping, and describe the cost reduction efforts for largescale studies.
Re-sequencing for mutation discoveryThe ability to sequence a large number of DNA samples rapidly and accurately for detection of all possible mutations is a critical goal in biomedicine. DNA mutations can be classified as known or unknown mutations. If the mutation is known, the region containing the mutation can be analyzed at or nearby the mutation site. If the mutation is unknown, re-sequencing of the region for determination of the nature of the mutation is required. When DNA from biopsy material is being resequenced, a quantitative method for determining the ratio between wild and mutated template is desired. When analyzin...