Repost re: infectivity of RNA/DNA

[ncel]

On Mon, 15 May 1995, C. Maples wrote:
> 
> These same RNAses are present in the environment as well as the lab.  The 
> 'stable RNA's' are stable because of their structure which differs from 
> that of messenger RNA (for the most part).  Messenger RNA's are typically 
> what interests a lab, and these are the unstable RNA's.
> -Charles

What do you mean by "environment"? RNases don't just float around in the
air. Contrary to what is the case with human skin, to my knowledge, no
RNases have been shown to be present on the surface of plant leaves. I
wondered about that years ago, when I found no correlation between the
infectivity of free tobacco mosaic virus (TMV) RNA (which, by the way, is
not significantly more resistant to inactivation by RNases than are mRNAs)
when rubbed onto leaves of various plant hosts and the level of RNases
detectable in leaf homogenates of these species. Further experimentation
revealed that no RNases could be detected in "washings" from the surface
of carborundum-dusted, rubbed (that is, mock inoculated) leaves,
regardless of the level of RNases in homogenates. Clearly, as is now well
known, of course, in the intact cell, RNases are localized in subcellular
components and the invading viral RNA is not exposed to them under the
conditions of inoculation. 

I am not sure I understand your argument re "stable" vs. "unstable" RNAs. 
What determines the level of stability? Secondary structure? If so, how 
about dsRNA which, at low ionic strength (but without strand separation),
is readily hydrolyzed by RNase A? Also, I believe that, in virology labs 
at least, RNAs other than mRNAs are of considerable importance.
Ted