Random cleavage of DNA by methods other than using restriction endonucleases

Random cleavage of DNA by methods other than using restriction endonucleases 

The set of DNA fragments produced by a restriction enzyme are of course non-random in the sense that the specificity of the enzyme 

In this experiment the Pstl fragment was first digested with DNAase II in sodium acetate buffer, pH 4.7 at room temperature and the reaction halted by chilling and extraction with phenol. After precipitation the DNA was electrophoresed on an 8% polyacrylamide gel and a slice of gel, corresponding to fragments of chain length 150-250 nucleotides cut out and eluted. The 3 -terminal phosphates were removed by treatment with alkaline phosphatase and, after denaturation and removal of the phosphatase with phenol, the DNA was reprecipitated and dissolved in a small volume of water. 

Products are a mixture of fragments with flush ends and 3 -or 5 - extensions 

A relatively large excess of linker is required to minimize end to end ligation of the DNAase II fragments yielding false sequences. 

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