Repost re: infectivity of RNA/DNA

[C. Maples]

On 19 May 1995, ncel wrote:

> 
> 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. 

This is just my 2 cents..... :)

My understanding of the source of the RNase from hands that molecular 
biologists fear is that they are from bacteria (living and dead).  I also 
thought, but cannot confirm, that there are non-protein agents that can 
degrade RNA such as NaOH and certain transition metals (has anybody 
heard of this?).  Since these reagents are ubiquitous (more or less), 
they should be found outside the lab in the environment.  

> 
> 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  

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.  

regards,
Charles