• Journal of Microbiology and Biotechnology
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• v.4 no.4
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• pp.250-255
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• 1994

Wild-type and four mutant R100 merR genes were cloned and the proteins overproduced under tac promoter control of pKK223-3. His118Ala, Cys117Ser, Cys126Ser, and wild-type MerR were successfully overproduced although amino-terminal 14 amino acids deletion mutant MerR was not successful. The amount of overproduced wild-type MerR protein as well as other mutant MerR was between 15%-20% of the total protein. The protein was able to be purified up to 95% homogeneity. Specific DNA-protein blotting experiments showed that the 95 bp operator containing DNA fragment could bind to Cys126Ser, His118Ala, and wild- type MerR, but not to Cys117Ser. These results were consistent with the previously reported complementation experiment results that His118Ala, Cys126Ser, and wild-type MerR could repress the mer operon but Cys117Ser could not.

• Journal of Microbiology and Biotechnology
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• v.4 no.4
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• pp.245-249
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• 1994

An amino-terminal 14 amino acids deletion and three site-directed mutations were created to investigate the mechanism of induction and repression of MerR regulatory protein in R100 mer operon from gramnegative Shigella flexneri. The amino-terminal 14 amino acids deletion, Cysl17Ser, and Cys126Ser mutations abolished the inducibility of the mer operon and the Hisl18Ala mutation resulted in the reduction of inducibility (about 9.1 % remaining) in complementation experiment in the presence of $Hg^{2＋}$ at subtoxic level ($1\mu M$). The complementation experiment with $Hg^{2＋}$ absent showed that Hisl18Ala, Cys126Ser, and wild-type MerR could repress the operon but Cysl17Ser could not, and the amino-terminal deletion mutant could neither induce nor repress the R100 mer operon.