Journal of Molecular Biology
Volume 6, Issue 1, January 1963, Pages 16-21, IN1
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An electrophoretic study of mutationally altered a proteins of the tryptophan synthetase of Escherichia coli

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The mutationally altered A proteins (tryptophan synthetase) of nine single mutants and three double mutants of Escherichia coli have been examined by electrophoresis in Polyacrylamide gel and on cellulose acetate. The A proteins from seven of the single mutants studied exhibited charge differences from the wild-type A protein. The mutationally induced amino acid substitution in one of these seven A proteins is known and the change in charge observed with this protein is consistent with the amino acid substitution. The A protein of one double mutant had a charge which was intermediate between that of the two corresponding single-mutant proteins. However, the mobilities observed with two other double-mutant proteins were not consistent with those expected on the basis of electrophoretic analyses with the corresponding single-mutant proteins. Furthermore, the electrophoretic mobilities of these two double-mutant proteins relative to the wild-type A protein were different on cellulose acetate and in Polyacrylamide gel. Possible explanations of the inconsistent mobilities are offered. The results obtained are correlated with the restricted location of the corresponding mutant sites on the genetic map of the A gene.

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Present address: Max-Planck-Institute für Zellchemie, Karlstrasse 23, Munich, Germany.

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