request advice on RNA storage

[Robert Hewitt]

Dear internetter, 

I'm presently preparing total RNA for Differential Display, and mRNA for 
Northern blotting.  I'm new to this field, but know that RNA preparation 
is not always straightforward. If anybody could give me advice about RNA 
storage, I'd be very grateful.  Here are some questions that I am stuck on:

1. What is the best way to store RNA long term?  Is it OK to store in 
water at minus 70 degrees C?  Does RNA degrade in these conditions over a 
period of months?  Would it be better to store while precipitating in 
ethanol, or as a dry pellet at minus 70 degrees C?

2. Are polyA tails more susceptible to degradation than the rest of the 
mRNA molecule?  I'm told that mRNA preparation works best with freshly 
prepared total RNA - is this because poly A tails are readily lost on 
storage?  Would such loss be due to trace RNase contamination, or 
freeze-thaw?

Thank you in advance for any help,

Robert Hewitt