I am running a 1% agarose gel for separation of the different forms of pBR 322 and I see a band in the well.

I do not quite understand the reason why I should see a band which shows almost zero electrophoretic mobility.

A colleague told me that it could be the presence of genomic DNA.

I bought the plasmid from New England BioLabs (expressed from E.coli)

Thanks and kind regards