I wanted to know if the peculiarities I had long-ago noticed in DNA of competent cells were reproducible. So yesterday I grew some wildtype cells in rich medium. Some of them I collected during exponential growth ('log phase', cell density about 2 x 10^9 cells/ml), some when the culture was approaching its final density ('stationary phase', about 10^10 cells/ml), and some I transferred to the competence-inducing starvation medium while they were in log phase. I prepared chromosomal DNA from all three treatments, and then incubated it either in the standard DNA buffer TE (10 mM Tris pH 8, 1 mM EDTA) or in the mung bean nuclease buffer that had previously given anomalous results for competent-cell DNA. DNA in the mung bean nuclease buffer sat at room temperature for about an hour, with and without being heated to 65 °C for 10 minutes. Then I ran all the DNAs in a gel to check their condition.
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So I can put this old result out of my mind, and get to work on my planned competence and phage recombination assays.
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