DNAse at pH5?

[James Graham]

There is a legacy here whose source I cannot unearth -that total 
RNA samples be treated with DNAse at pH 5 rather than neutral pH to 
eliminate contaminating DNA.

All I have seen so far is that Boehringer gives their DNAse activity
units in terms of action in a pH5 buffer, and that indeed my RNA 
emerges from such a DNAse treatment intact, while not fairing at all
well when treated at a more conventional pH (8.0). I have no idea yet 
what kind of DNA removal this former treatment achieves, being a pH at 
which only some 10-20% of DNAse I activity would be expected to remain.

Perhaps residual endogenous RNAses are differentialy inhibited 
to a greater extent than DNAse at this pH? Is it a typo? :)

Thanks again,

Jim
J. Graham PhD 
Biology Department 
Washington University of St. Louis 

(PS. Not interested in binding matrices or proprietary columns suggested 
to selectively eliminate DNA- but might like to hear about other approaches.)