What is the role of potassium acetate in the alkaline lysis method of plasmid extraction?

Earlier I was thinking its role is to shield plasmid DNA (the same as sodium acetate in genomic DNA extraction). When 100% ethanol is added, it the DNA precipitates and then we remove potassium ions from the pellet using 70% ethanol.

However, I have read that potassium acetate does not have the same function as sodium acetate in genomic DNA isolation but, rather, is a neutralizing agent which helps small plasmid DNA to renature.

I am bit confused about the role of potassium acetate and why sodium acetate cannot be used instead.


1 Answer 1


The alkaline lysis method of plasmid purification involves the addition of sodium dodecyl sulfate to lyse the cells and sodium hydroxide (a strong base) to denture the DNA. Potassium acetate is then added for two reasons:

  1. The acidic acetate buffer neutralizes the solution and allows catenated plasmids to renature.
  2. Potassium dodecyl sulfate is poorly soluble in water. Adding potassium to solutions of dodecyl sulfate precipitates it, thus facilitating its removal.
  • $\begingroup$ Okay..but then...how plasmid DNA is concentrated...like in genomic dna extraction..sodium ion forming shield around dna and on adding 100% ethanol interaction getting more stonger and then pelleting it.. $\endgroup$
    – Krishi1234
    Mar 28, 2018 at 10:22
  • $\begingroup$ So isn't potassium acetate playing that role here?....then why we are adding 100%ethanol here too? $\endgroup$
    – Krishi1234
    Mar 28, 2018 at 10:23
  • 1
    $\begingroup$ @Krishi1234 You can precipitate plasmids with ethanol and salt. You need to post your protocol in order for us to tell what the potassium acetate is being used for. I answered based on the standard alkaline lysis method, but if you’re adding KAc and ethanol at the same time then that’s a different story. $\endgroup$
    – canadianer
    Mar 28, 2018 at 15:42

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