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FEMS Microbiol Lett. 2000 Apr 15;185(2):117-21.

Homocysteine thiolactone is a positive effector of sigma(S) levels in Escherichia coli.

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Department of Bacteriology, University of Wisconsin-Madison, Madison, WI, USA.


sigma(S) is a regulator of the stationary phase response in Escherichia coli. Multi-copy suppressors were sought in a strain with decreased levels of sigma(S) and one such suppressor was found to encode HsrA, a putative efflux pump. Multi-copy expression of hsrA was shown to lead to accumulation of homocysteine, which is predicted to cause an increase in homocysteine thiolactone (HCTL) levels. A direct correlation between HCTL levels and sigma(S) accumulation was observed both in mutants and during normal cell growth, leading to the hypothesis that HCTL is a physiologically relevant positive effector of sigma(S) levels in vivo.

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