Capillary DNA sequencing
Separation of DNA products from a DNA
sequencing reaction by conventional gel
electrophoresis creates a number of challeneges,
including preparing gels, practical problems of loading
multiple reactions manually in a single gel,
differential migration rates of products across the
width of the gel, and long electrophoresis times (8 ~12
hrs for long fragments). An alternative separation
method uses (A) ultra-thin capillaries,
pre-packed with a a gel-like matrix material. (B)
Because of the extremeley high voltage applied,
electrophoretic separation occurs in a few hours, and,
unlike gel electrophoresis, the capillary matrix can be
reused multiple times. [Right] Fragment mobilities in
sets of eight capillaries are monitored simultaneously
at an immobile detector window, so that the
order in which succesively longer fragments pass the
detector automatically determines the sequence.
A capillary array includes 48~96
capillaries that are loaded automatically by a robot
from a stack of 96-well reaction plates, renewed
as required, so that sequencers can be run continuously.
Sequence data (chromatograms)
are fed directly to a central computer server, and
may be downloaded remotely at labs hundreds or
thousands of kilometers from the facility. Large-scale
sequencing laboratories such as those used in the Human
Genome Project may have dozens or hundreds of
machines operating 24-7. Economies of scale may
make it cheaper to out-source DNA sequencing to
such a facility than to purchase, maintain, and staff a
DNA sequencer locally.