A possible problem associated with the high voltage electroporation of very large DNA fragments such as YACs is that the molecules are most likely sheared before they have a chance to enter the cell. Lower voltage experiments with the Gene Pulser apparatus (which generates an exponential decay pulse) have a less disruptive effect on large DNA molecules, but they also yield lower transformation efficiencies.3,4 The use of alternative waveforms may improve on current results.6 The S. cerevisiae strain used here (AB1380) is traditionally employed in PEG-spheroplast transformations and we do not know whether this strain is also a good electroporation candidate. Other strains that have proven to yield high transformation rates might further improve the results presented here.
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