Repost re: infectivity of RNA/DNA

[ncel]

> On Mon, 15 May 1995, C. Maples wrote:
> 
> According to the "Molecular Cloning Manual" by Maniatis et al, RNase A 
> will cut dsRNA at sites of a mismatched bp, otherwise the helix is 
> resistant.  Yes, secondary structure, or perhaps a higher level, 
> contribute to RNA stability, e.g. rRNA and I believe viroids have 
> intricate secondary structure.  PolyA tails contribute to mRNA 
> stability.  I would wager that genomic RNA is more similar to mRNA than 
> other kinds of RNA, if not identical to a primary transcript (with at 
> least one exception with viroids), so I lumped genomic RNA and mRNA 
> together.  Since genomic RNA is sensitive to degradation, they are 
> typically covered with a nucleoprotein that functions, at least in part, 
> to protect the RNA.  

	You are correct, of course, regarding the resistance of dsRNA to 
RNase A and the Maniatis quote. Having worked at one time in the dim past 
with plant viral dsRNA, I remember that proper ionic strength was 
essential to the resistance of this RNA to RNase A. I regret not being 
able to immediately document this with a proper reference; the 
following must do for the moment: R.E.F. Matthews in "Plant Virology", 
Second ed., writes (p. 85): "The ds structure makes the phosphodiester 
backbone of the RNA strands resistant to attack by pancreatic RNase 
provided the reaction is carried out at an appropriate pH and ionic 
strength." Evidently, in the Maniatis book, it is assumed that an
appropriate pH and ionic strength are used.  
	You are also correct that secondary structure affects 
susceptibility to RNasess, but even viroids with their highly stable 
secondary structure are inactivated by RNase A (even when incubated in their 
native, highly base-paired, conformation). 
	Do you have a ref. on the increased resistance of polyA-tailed 
RNA to RNase? Does this apply to RNase A?
	Regards,
	Ted Diener