Molecular and General Genetics MGG

, Volume 250, Issue 5, pp 523–532 | Cite as

Requirement for two conserved cysteine residues in the Ada protein ofEscherichia coli for transactivation of theada promoter

  • A. Taketomi
  • Y. Nakabeppu
  • K. Ihara
  • D. J. Hart
  • M. Furuichi
  • M. Sekiguchi
Original Paper


Cysteine residue 69 of theEscherichia coli Ada transcription factor, which accepts a methyl group from methylphosphotriester in methylated DNA, was substituted by each of 19 other amino acids. Only the mutant Ada (C69H), carrying a histidine substitution of Cys69, exhibited a limited degree of transactivating potential for theada promoter inE. coli cells although the mutant protein was completely devoid of methylphosphotriester-DNA methyltransferase activity. Using a multicopy plasmid system for the expression of Ada protein, we have shown that Ada C69H has a transactivating capacity equivalent to that of wild-type Ada protein in the absence of an alkylating agent. This indicates that the zinc-binding capacity of histidine at residue 69 is likely to be sufficient for Ada to recognize and bind to theada promoter. Furthermore, transactivation of theada promoter by Ada C69H was enhanced up to 6-fold by treatment with methylating agents. An additional substitution was made with alanine in Ada C69H, replacing Cys321, the site for acceptance of a methyl group from O6-methylguanine and O4-methylthymine residues in DNA, with alanine. This renders the protein completely inactive as a methyltransferase but this derivative is constitutively active as a transactivator for theada promoter. Therefore, acquisition of a methyl group at Cys321 apparently enhances the transactivating capacity of Ada protein on theada promoter. We propose that the transcription-regulating function of Ada protein is under dual control by methylation of cysteine residues at positions 69 and 321; the former enhances DNA binding, while the latter enhances the transactivating capacity of the protein.

Key words

Adaptive response Alkylating agent Methylation O6-Methylguanine DNA methyltransferase Zinc protein 


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Copyright information

© Springer-Verlag 1996

Authors and Affiliations

  • A. Taketomi
    • 1
  • Y. Nakabeppu
    • 1
  • K. Ihara
    • 1
  • D. J. Hart
    • 1
  • M. Furuichi
    • 1
  • M. Sekiguchi
    • 1
  1. 1.Department of Biochemistry, Medical Institute of BioregulationKyushu UniversityFukuokaJapan

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