EDTA in hybridization?

[In C. Kim]

Hi all,

I have a question on the role of EDTA for Southern/Northern 
hybridization.  Some hybridization buffer contain EDTA, and some don't.  
For example, Church hybridization buffer includes 1 mM EDTA.  My 
questions are:

	a) Is EDTA necessary for optimal hybridization?
	b) If so, what does EDTA do?  
	
Thanks.

--In C. Kim