PEG in ligations

[nsaunders at molbiol.ox.ac.uk]

Hi,

As far as I know you're right in that PEG effectively reduces the "free water" 
concentration; this results in macromolecular crowding of the DNA molecules, 
so helping to bring them together if dilute DNA solutions are used. Other 
agents do this too e.g. hexamine cobalt chloride (see Maniatis).

I think use of PEG is also recommended for blunt-end ligations, as these tend 
to be less efficient and it helps to try and bring the ends together, though 
I've never seen a big difference. As for amounts, I think PEG 6000 or PEG 8000 
will do, and I think it's 15% final concentration in the ligation.

Neil Saunders