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Hove, Arthur (ed.) / Wisconsin alumnus
Volume 62, Number 14 (June 1961)

Portrait of a virus,   p. 17


Page 17


PORTRAIT
of a Virus
The "umbrella-like" circles in this photograph are the smallest
known viruses, recently
purified, analyzed, weighed, and photographed at the University of Wisconsin.
T HE SMALLEST VIRUS known to
    science has been purified, weighed,
chemically analyzed, photographed and
taken apart at the University of Wis-
consin.
   UW Prof. Paul J. Kaesberg and bio-
chemistry graduate student Larry E.
Bockstahler believe their work on this
project could lead to new knowledge of
viruses that cause hundreds of diseases.
Some of these virus-caused diseases, Dr.
Kaesberg said, are cancer, polio, rabies
and hoof-and-mouth disease. Just as im-
portant, the simplicity of the virus and
its relatively small amount of hereditary
material could lead to new information
about heredity.
   "What we have now," said Dr. Kaes-
berg, "is a virus that can be grown
easily and in large quantities; one that
is safe to work with; one that seems
typical, and much like polio or the
small cancer-producing viruses. Maybe
studies of how this virus infects, and
Wisconsin Alumnus, June, 1961
what effects it has on other cells, will
carry over to considerations of other
viruses."
   The virus is Bromegrass Mosaic
Virus, BMV for short, which causes
mottling and streaking of the leaves of
smooth Brome Grass, a common prairie
grass. The virus can infect grain crops
like wheat, rye and corn. This much
had been known for some years, but
the surprising smallness and simple
structure of the virus was a lucky acci-
dent, helped along considerably by the
researcher's scientific curiosity. Their
research in UW's Department of Bio-
chemistry was supported by Wisconsin
Alumni Research Foundation (WARF)
and the National Institutes of Health.
  More than two years of work went
into the final scientific "portrait" of the
virus drawn by Dr. Kaesberg and Bock-
stahler. They found a virus with a
molecular weight of 41     million, a
little smaller than the next smallest
virus (molecular weight 51/2 million)
and less than half the size of the quite
small polio virus whose molecular
weight is about 10 million.
   By comparison, typical viruses that
attack bacteria are much larger, more
complicated, and have heads and tails.
One typical bacterial virus called T-2
has a molecular weight of 240 million.
This makes the whole BMV virus only
about twice as thick as the tail of the
T-2 virus and a little less in weight
than T-2's tail alone.
- Dr. Kaesberg estimated that about
3,000 BMV viruses side by side would
make a pile as thick as the page you
are now reading.
  More important, perhaps, is that the
BMV plant virus contains only about
half the amount of hereditary material
that the small polio virus does, and only
about one-hundredth the amount found
in a typical bacterial virus. The heredi-
tary materials-either DNA or RNA-
are the substances which carry the chem-
ical information on how to reproduce.
   Viruses are parasites. They cannot
reproduce themselves, but must infect
other organisms and force them to learn
the job of virus-breeding. Viruses
apparently achieve this sabotage by
attaching themselves to their "host"
cells and passing a chemical lesson on
reproduction through their RNA or
DNA. Viruses may be rod-shaped,
cylinder-shaped or round, but generally
they are little more than a certain
amount of hereditary material enclosed
in a protecting "overcoat" of protein.
   Being spherical, BMV is similar in
structure to the many larger viruses that
cause hundreds of diseases. One of these
is the polyoma virus-the best known
of the viruses that cause cancer in
experimental animals.
   "In basic virus work the structure is
one big answer we look for," said Dr.
Kaesberg. "For most of these spherical
viruses, we feel sure they're made of
sub-units, but we know only roughly
how many there are. For the animal
viruses we know nothing on this.
Ideally, we'd like to know the structure
of the other spherical viruses and how-
they attach themselves to other cells andc
infect them. This all depends on their-
structure, and the BMV virus seems not-
unlike some of these other viruses inm
structure."
17


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