FAQ: Why do I see a smear above my plasmid band on an agarose gel?

The presence of a smear at a higher molecular weight than the plasmid band may indicate genomic DNA is contaminating the prep. While not common, genomic DNA can be sheared during lysis and co-purify with the plasmid. Vigorous shaking or vortexing after addition of buffer B2 will produce sheared genomic DNA and should be avoided. If the lysate is very viscous and does not mix well, use less cells for the miniprep.