One way to do an yeast transformation is by using lithium acetate, a single-stranded carrier DNA, and PEG [(1)](http://www.nature.com/nprot/journal/v2/n1/full/nprot.2007.13.html). I was wondering why is the polyethylene glycol important for the efficient transformation. How does it affect the take-up of the foreign DNA? Yamakawa et al (2) showed that PEG is essential for the recovery of the cells but I couldn't access that paper to read more about it.

[1. R Daniel Gietz & Robert H Schiest (2007). High-efficiency yeast transformation using the LiAc/SS carrier DNA/PEG method](http://www.nature.com/nprot/journal/v2/n1/full/nprot.2007.13.html)

[2. Yamakawa, M., Hishinuma, F. and Gunge, N. (1985). Intact cell transformation of Saccharomyces cerevisiae by polyethylene glycol. Agric. Biol. Chem. 43, 869-
871.](http://www.ncbi.nlm.nih.gov/pubmed?term=Intact%20cell%20transformation%20of%20Saccharomyces%20cerevisiae%20by%20polyethylene%20glycol)