About Norther Blot - QUESTIONS (Aug/31/2004 )

Hi everyone, I will start Northern Blot, but after reading some protocols, I have some questions:

1) what is the use of Denhardt's-solution and Formamide?
2) why are high salt buffers like 10XSSC or 6XSSC used in the protocol?
3) what is the usual length of probes, is it made by PCR? are there some criteria for designing probes?
4)It is said in Northern Blot protocols that the transferred membrane can not be dried out if you want to strip it. But, if I expose it for 48 hours at -70 C or at room temperature, how can I be sure that the membrane is still moist?

Thanks!

3) what is the usual length of probes, is it made by PCR? are there some criteria for designing probes?
Even synthesized oligos of 25 nt or longer can be used as probe.

4)It is said in Northern Blot protocols that the transferred membrane can not be dried out if you want to strip it. But, if I expose it for 48 hours at -70 C or at room temperature, how can I be sure that the membrane is still moist?
You can seal your membrane in a plastic bag and store it.