Catenanes (was Re: Gentle Plasmid prep protocol needed)

Frank O. Fackelmayer fof1 at
Thu Jul 16 09:47:49 EST 1998

Dr. Duncan Clark wrote:
> I always thought that multimers only formed in recA+ E.coli and not in
> recA-. Given that the majority of standard lab strains are recA- you
> don't really see multimeric forms in any high proportion. I don't recall
> seeing them say when using Invitrogen TA vectors (pUC derived) when
> using the recA- TOP10 cells even when grown for 24 hours in LB.
We mostly use XL-1 bacteria that are recA-, and we do see catenanes from time
to time. But yes, catenane formation is not as common as in "old" strains. I´m
not sure if the recA genotype is relevant for catenane formation (do you have
hard data on that?). Rather I suspect the slower growth of these "modern"
strains of bacteria to be the reason for lower percentage of catenanes.
Possibly gyrase activity is then sufficient for an effective separation of
replicated plasmids. In "old" strains of E.coli (TG1 for example), growth is
much faster (compare the colony sizes!), and all gyrase might be engaged in
chromosome replication. Just a thought...


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