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plants had appeared in nature rather than in Marty's laboratory they would
have died without reproducing.
Susan Lindquist and her colleagues at the Whitehead Institute in Cam-
bridge, Massachusetts, have gained further insights into mutations that have
such large ef ects by working with the fruit fl y, Drosophila melanogaster . Under
the microscope this tiny fl y is revealed to be a complex and jewel-like crea-
ture, with bright red faceted eyes, subtly patterned wings, and antennae that
allow it to home in on the tiniest chemical signals from that slice of canta-
loupe you are eating.
Lindquist and Suzanne Rutherford examined fruit fl ies that make a defec-
tive form of a protein called a chaperonin. 15 Chaperonins are proteins that, as
their name suggests, act as guardians of other proteins.
Many of the proteins in our cells are extremely fragile. When they are
being synthesized by the cellular machinery they tend to fl op around like
newborn babies. Chaperonins bind fi rmly to these delicate proteins during
the critical birth process, coercing them to take the right shape so that they
can play the correct role in the cell's development. Like Mary Poppins, the
chaperonins permit no nonsense from their unruly young charges. They
make sure that their protein pupils, many of which play important regula-
tory roles, get to their proper place in the cell and bind to the right parts of
other proteins or to the right regions of DNA, without the molecular equiva-
lent of making funny faces in the process.
The chaperonin that Rutherford and Lindquist investigated is a “heat-
shock protein” called Hsp90. High temperatures are dangerous to proteins,
and many organisms, ourselves included, synthesize plentiful amounts of
these heat-shock chaperonins to protect our other proteins under these
extreme conditions.
Fruit fl ies cannot survive if they make no Hsp90, so Rutherford and
Lindquist used fl ies that carried one damaged and one normal form of the
Hsp90 gene. These mutant fl ies made half as much of this chaperonin as
normal fl ies. This small genetic change was enough to cause a few of the
fl ies to develop abnormally. Among the many dif erent kinds of abnormali-
ties, some of these fl ies had misplaced and misshapen eyes, while others had
wrinkled wings.
 
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