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One way to do an yeast transformation is by using lithium acetate, a single-stranded carrier DNA, and PEG (1). 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

2. Yamakawa, M., Hishinuma, F. and Gunge, N. (1985). Intact cell transformation of Saccharomyces cerevisiae by polyethylene glycol. Agric. Biol. Chem. 43, 869- 871.

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  • $\begingroup$ PEG causes fusion of protoplast (in general lipid-bilayers) $\endgroup$
    – user1393
    Commented Sep 12, 2012 at 15:38
  • $\begingroup$ I found this article that might answer your question: Shigeyuki Kawai1, Tuan Anh Phan1, Emi Kono1, Kazuo Harada2, Chihiro Okai2, Eiichiro Fukusaki2, and Kousaku Murata1 (2009). Transcriptional and metabolic response in yeast Saccharomyces cerevisiae cells during polyethylene glycol-dependent transformation. Journal of Basic Microbiology 2009, 49, 73 – 81 I think this is the correct link: onlinelibrary.wiley.com/store/10.1002/jobm.200800123/asset/… $\endgroup$
    – user3442
    Commented Apr 23, 2013 at 10:21
  • $\begingroup$ It is more of a comment, but I can not add one due to my rep points. In addition to what others have already added, I was also told that PEG helps in stabilising the yeast cells, thereby increasing their recovery. I can not share the Nature Protocol paper from Gietz et al, but this is a book chapter from the same authors on the same topic: researchgate.net/profile/R_Gietz/publication/… $\endgroup$
    – ktyagi
    Commented May 5, 2015 at 18:18

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http://www.protocol-online.org/biology-forums/posts/26634.html

I found this link - it says 'we don't really know'. It says PEG binds DNA, I assume shielding the membrane from its negative charge and allowing internalization to happen.

I would guess that the amphipathic nature of PEG, being partly hydrophobic, also helps soften up the membrane. Interestingly, if you increase the PEG concentration beyond the limits, it decreases the efficiency of the procedure.

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I assume it has an analogous function in ligation buffers. There it apparently takes up a large proportion of the volume and thereby increases the chance of interaction between bits of DNA.

In a transformation buffer it should increase the chance of DNA getting into a cell. Unfortunately the only reference I found for this was at Bitesizebio: http://bitesizebio.com/20/5-dna-ligation-tips/

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