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Griffith’s
experiments further defined the gene but brought us no
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closer
to understanding the composition of genes.
Then in the 1940s a
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group
of scientists at Rockefeller University carried out a study to
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finally
identify the genetic material. Again
working with
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Dipplococcus
pneumonia, these investigators, Avery, McCarthy, and
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MacLeod
first showed that they could convert non infectious rough (R)
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pneumococcus
into smooth (S) virulent pneumococcus by mixing heat
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killed
(S) with live (R) and plating them onto plates got smooth
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bacteria. This became their assay. Next they isolated the material in
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(S)
that transformed (R). They began
with (S) bacteria and isolated
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DNA
by alcohol precipitating and then spooling it out. This material
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was
able to transform (R). This material
was exhaustively extracted to
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remove
any protein. And again it
transformed. Next they treated this
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material
with RNAse, no effect, protease, no effect and finally DNAse.
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The
DNAse killed the transforming activity and so they concluded that
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DNA
was the genetic material. This was
not widely accepted.
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