Checking Transformation Efficiency of Chemically Competent Cells

Adapted from Molecular Cloning: A Laboratory Manual 3rd Ed., Sambrook and Russell (2001)



  • Shaking Incubator or Shaking Platform and 1L flask clamps
  • 42C Heating Bath or Block
  • 37C Incubator
  • Colony Counter


  • Agar plates with appropriate antibiotic

Buffers and Solutions:

  • Competent cells prepared using the Inoue method
  • 10pg / μL solution of a standard plasmid (e.g. pUC19)
  • SOC Medium


  1. ) Transform 10pg of a standard plasmid (e.g. pUC19) in 50μL of cells using the standard transformation protocol.
  2. ) Plate 50uL of transformed cells in triplicate on appropriate antibiotic
  3. ) Grow plates overnight, and count colonies the next morning
  4. ) Average colony counts for the three plates; efficiency = (# colonies) x 106 cfu / μg
  5. ) Expected efficiency for the Inoue protocol is 1-3 x 108 colonies / μg of plasmid

-- Main.KateElston - 25 Oct 2018

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Topic revision: r2 - 26 Oct 2018 - 20:35:15 - Main.KateElston
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