What's the role of PEG in transformation - Does the size of the PEG matters? (Apr/23/2007 )

I have a transformation protocol that says I need to use 30kD PEG in the transformation buffer while my lab only has 44kD PEG. So What is PEG doing in the transformation? Can I just go ahead using the 44kD PEG or do I have to order some new one with the right size?

The exact role of PEG isn't still known exactly. It binds well to DNA (e.g. you can precipitate DNA with PEG in plasmid preparations) and seems to work as a carrier that also is supposed to make little holes in the cell membranes...

I think it won't matter to try your PEG4400. In a paper of Chung et al. (1989) they compare different PEGs and find PEG3350 and PEG8000 as best working for E.coli.

Greetings,
Chakchel