niiicholas
Posts: 319
Joined: May 2002
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Good little one that Ian Musgrave posted at t.o. in rebuttal to a creo reiterating Behe's argument regarding Ken Miller's citation of Barry Hall's work on lactose metabolism:
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G'Day All
Address altered to avoid spam, delete RemoveInsert
On Thu, 3 Apr 2003 17:59:50 +0000 (UTC),
seanpitnospam@naturalselection.0catch.com (Sean Pitman M.D.) wrote:
>Evolving Rube Goldberg Machines
>http://naturalselection.0catch.com/Files/Rube%20Goldberg.html
[enormous snip]
>But what if the E. coli had
>not been so fortunate as to have this spare tire gene? What would
>have happened then? Hall wondered about this himself. He then
>deleted the spare tire gene as well as the lacZ genes. Would there be
>lactase evolution now?
See Matsumura I, Ellington AD. In vitro evolution of
beta-glucuronidase into a beta-galactosidase proceeds through
non-specific intermediates. J Mol Biol. 2001 Jan 12;305(2):331-9)
where they have evolved a beta glactosidase from an enzyme other than
the "spare tyre". I believe I have directed you to this paper before.
link to thread
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Da paper:
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Matsumura I, Ellington AD. In vitro evolution of
beta-glucuronidase into a beta-galactosidase proceeds through
non-specific intermediates. J Mol Biol. 2001 Jan 12;305(2):331-9
The Escherichia coli beta-glucuronidase (GUS) was evolved in vitro to catalyze the hydrolysis of a beta-galactoside substrate 500 times more efficiently (k(cat)/K(m)) than the wild-type, with a 52 million-fold inversion in specificity. The amino acid substitutions that recurred among 32 clones isolated in three rounds of DNA shuffling and screening were mapped to the active site. The functional consequences of these mutations were investigated by introducing them individually or in combination into otherwise wild-type gusA genes. The kinetic behavior of the purified mutant proteins in reactions with a series of substrate analogues show that four mutations account for the changes in substrate specificity, and that they are synergistic. An evolutionary intermediate, unlike the wild-type and evolved forms, exhibits broadened specificity for substrates dissimilar to either glucuronides or galactosides. These results are consistent with the "patchwork" hypothesis, which postulates that modern enzymes diverged from ancestors with broad specificity.
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Edited by niiicholas on April 04 2003,21:27
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