Bacterial artificial chromosome (BAC) libraries play a pivotal role in genomics studies. A crucial step in BAC library construction is the transformation of Escherichia coli by electroporation. Absolute efficiency (cfu/μg DNA) is affected by a number of factors including the topological form and treatment of DNA samples. Here we report a simple new protocol using tRNA assisted precipitation that increased transformation efficiency by 70-fold for BAC ligations and up to 400-fold for plasmid ligations. The mechanism may involve altering or stabilizing the topographical form of the DNA molecules.
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