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From: roy@phri.UUCP (Roy Smith)
Newsgroups: net.med
Subject: Re: attacking viruses
Message-ID: <404@phri.UUCP>
Date: Wed, 14-Aug-85 16:08:08 EDT
Article-I.D.: phri.404
Posted: Wed Aug 14 16:08:08 1985
Date-Received: Tue, 20-Aug-85 01:20:13 EDT
References: <2617@amdcad.UUCP>
Organization: Public Health Research Inst. (NY, NY)
Lines: 47

Phil Ngai  says:
> in recombinant DNA research they use agents (a form of RNA?) which cut the
> genes at precise points. [...]  Could we simply employ the right agents to
> cut up the genes in nasty viruses? [...] The cutting agents seem to be
> programmed to cut at precise places, which means they should be able to
> attack the desired virus and nothing else.

	The agents are called restriction endonucleases or, more commonly
restriction enzymes, and are made of protein, not rna.  This detail aside,
they do indeed cut at precise places; the accuracy with which they find
their proper cut sites and reject all others is staggering.  Because of
this, you can use them to cut-and-paste dna in the lab using them as the
scissors.  It's hard to imagine *anything* being done in a molecular biology
lab without them.

	These enzymes exist for exactly the reason you want to use them as
therapeutic agents.  Certain bacteria make restriction enzymes which are
programmed to cut dna at nucleotide sequences which don't appear at all in
that species' own dna.  Thus, the bacteria are immune from being turned into
dna salad by their own enzymes.  However, when foreign dna gets into the
cell, as happens when under attack by a virus, the enzymes go to work and
chop it up.  The concept is similar to making antibodies, though the
mechanisms are totally different.

	There are lot of problems, however, with using restriction enzymes
to treat viral infections in people.  First you would have to find a way to
get them into the body.  Orally won't work because they won't survive being
in the digestive system long enough to be absorbed.  I have no idea what
would happen if you administered them I.V. or I.M. -- Craig, care to take
this one?  Even if you got them where they had to go, you need the right
conditions of salt, pH, etc to work right.

	Those problems are trivial compared to the fact that we can't
program these enzymes ourselves (at least not yet).  All we can do is use
the ones that bacteria are kind enough to make for us.  To engineer a
restriction enzyme which would specifically attack viruses (or even just one
particular virus) while leaving our own dna alone is way beyond our current
technology.

> I'm an engineer, not a doctor.

	That's OK.  Us engineers are smarter than doctors anyway.  We just
don't make as much money.
-- 
Roy Smith 
System Administrator, Public Health Research Institute
455 First Avenue, New York, NY 10016