ASTRAL, a hyperspectral imaging DNA sequencer

We have developed a method for the partial automation of DNA sequence analysis. Fluorescence detection of the DNA fragments is accomplished by means of a fluorophore covalently attached to the oligonucleotide primer used in enzymatic DNA sequence analysis. A different coloured fluorophore is used for each of the reactions specific for the bases A, C, G and T. The reaction mixtures are combined and co-electrophoresed down a single polyacrylamide gel tube, the separated fluorescent bands of DNA are detected near the bottom of the tube, and the sequence information is acquired directly by computer.

A method and instrument for automated DNA sequencing without radioactivity have been developed. In spite of the success with radioactive labels there are drawbacks attached to the technique, such as hazards in the handling, storage and disposal of radioactive materials, and the considerable cost of the radiolabelled nucleoside triphosphates. In addition, there is deterioration of sample quality with time. A sulphydryl containing M13 sequencing primer has been synthesised and subsequently conjugated with tetramethylrhodamine iodoacetamide. The fluorescent primer is used to generate a nested set of fluorescent DNA fragments. The fluorescent bands are excited by a laser and detected in the gel (detection limit about 0.1 fmol per band) during electrophoresis, and sequence data from the four tracks are transferred directly into a computer. Standard gels, 200 mm wide with 20 sample slots have also been used. The device contains no moving parts. At present 250-300 bases can be read in 6 h. The system is capable of single base resolution at a fragment length of at least 400 bases.

A class of dyes, BODIPY fluorophores, has been identified for automated DNA sequencing that has improved spectral characteristics compared with conventional fluorescein and rhodamine dyes. Single and double BODIPY dye primers were characterized in commercially available DNA sequencers and showed uniform electrophoretic mobilities and high fluorescence intensities. The improved physical properties of BODIPY dye primers were demonstrated by direct base-calling from the unprocessed fluorescent signals and improved heterozygote analyses of mixed-base populations. The high sensitivity of BODIPY dye primers requires at least 33 percent less reagent consumed per reaction than conventional dye primers, which should affect the costs of large genome-sequencing efforts.