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Electrical conductivity across a polyacrylamide-filled capillary decreases during the separation of DNA sequencing fragments. This conductivity decrease is localized to the first few centimeters at the injection (negative) end of the capillary; no conductivity change is noted at the detection (positive) end of the capillary. The zone of decreased conductivity extends further into the capillary as the separation proceeds. The zone is most important for freshly prepared capillaries; capillaries used nine days after polymerization generate an insignificant current drop. The data are consistent with ionic depletion due to differences in transport numbers between the separation medium and the buffer reservoirs.

Terminal transferase is used to add a single fluorescently labeled dideoxynucleotide to double-stranded DNA prepared by restriction endonuclease action on a bacteriophage. The product is separated by capillary electrophoresis with both hydroxypropylmethylcellulose and non-cross-linked polyacrylamide. The reaction products generate single peaks for each fragment with hydroxypropylmethylcellulose. However, the higher resolution separation produced by non-cross-linked polyacrylamide shows that the product contains two components for each restriction digest fragment. This labeling technique should be useful in restriction fragment length polymorphism studies.

Capillary electrophoresis with laser-induced fluorescence detection (CE-LIF) is a promising new method for the analysis of protein sequencing products. It gives 10 zmol (1 zmol = 10(-21) mol) limits of detection (3 sigma) for fluorescein thiohydantoin (FTH) amino acids. We have developed a separation for the (FTH)-amino acid products generated from 18 of the 20 coded amino acids. The extremely low volume requirement associated with CE-LIF makes it incompatible with commercial sequencers. For this reason, we have also been developing a miniaturized sequencer that can be more easily coupled to our detection system. Both the CE-LIF system and the miniaturized sequencer are described.