A few weeks ago I asked for suggestions on why our lab might be having huge problems cutting genomic DNA from some Chlamy strains with enzymes that normally aren’t too fussy, particularly EcoR1 and Sal1. Thanks to the many people who answered. The most common response was that our DNA preparations might be contaminated with polysaccharides, apparently a common problem with preps from plant tissues too. Among the possible remedies I tried CTAB precipitation, mostly because it’s easy and cheap, and we do lots of DNA preps. The method I got was from Current Protocols in Molecular Biology: after a phenol-chloroform extraction, add to the supernatant 1/7 volumes of 5M NaCl, mix VERY well (otherwise the DNA precipitates), add 0.1 volumes CTAB solution (10% in 0.7M NaCl), and extract with an equal volume of 24:1 chloroform:isoamyl alcohol. This has totally eliminated our problems.