Sensing SAM

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Science  28 Mar 2003:
Vol. 299, Issue 5615, pp. 1947
DOI: 10.1126/science.299.5615.1947a

Living life as a single cell leaves little margin for error; an uneven supply of basic building blocks simply cannot be tolerated. A variety of feedback mechanisms that tightly couple biosynthetic pathways to metabolite concentrations have evolved, and how methionine is monitored in Bacillus subtilis illustrates the versatility of RNA. Upstream of the regions encoding proteins central to methionine metabolism lies a structural motif called the terminator, which promotes premature termination of transcription. This activity is regulated by an adjacent element that can switch between two secondary structural configurations, referred to as the antiterminator and the anti-antiterminator. What McDaniel et al. show in vivo and in vitro is that S-adenosyl methionine (SAM) binding to this element favors the anti-antiterminator structure, which unmasks the terminator and results in no transcript (and no protein) being made. This interaction is specific for SAM versus S-adenosyl homocysteine, raising the prospect of RNA-based crosstalk with methylation processes. — GJC

Proc. Natl. Acad. Sci. U.S.A.100, 3083 (2003).

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