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KMID : 0624620090420050293
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BMB Reports
2009 Volume.42 No. 5 p.293 ~ p.298
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Antagonistic effects Na＋ and Mg2＋ on the structure, function, and stability of mycobacteriophage L1 repressor
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Bandhu Amitava
Ganguly Tridib
Chanda Palas Kumar
Das Malabika
Jana Biswanath
Chakrabarti Gopal
Sau Subrata
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Abstract
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Temperate mycobacteriophage L1 encodes an unusual repressor (CI) for regulating its lytic-lysogenic switching and, in contrast to the repressors of most temperate phages, it binds to multiple asymmetric operator DNAs. Here, ions like Na＋, Cl?, and acetate? ions were demonstrated to facilitate the optimal binding of CI to cognate operator DNA, whereas K＋, Li＋, NH4＋, Mg2＋, carbonate2?, and citrate3? ions significantly affected its operator binding activity. Of these ions, Mg2＋ unfolded CI most severely at room temperature and, compared to Mg2＋, Na＋ provided improved thermal stability to CI. Furthermore, the intrinsic tryptophan fluorescence of CI was changed notably upon replacing Na＋ with Mg2＋ and these opposing effects of Mg2＋ and Na＋ were also noticed in their actions on the C-terminal fragment (CTD) of CI. Taken together, Na＋ appeared to be more appropriate than Mg2＋ for maintaining the biologically active conformation of CI needed for its optimal binding to operator DNA.
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KEYWORD
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Ions, Mycobacteriophage L1, Operator DNA, Repressor, Structure
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