Ribonuclease Protection Assays

[jon]

Hi--
I have a simple (I think) question about RPAs. I know that the 
RNAases used in these assays will cut digest ssRNA. Will they, then, 
cut where there is a single mismatch in the probe/RNA duplex? How 
about two or three mismatches in a row, or do they recognize a much 
larger motif? 

I'd like to know as I need to distinguish between two very similar 
allelic products. Thanks in advance, jon