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Science  17 Oct 2003:
Vol. 302, Issue 5644, pp. 359
DOI: 10.1126/science.302.5644.359b

Biological processes such as the handling of information and metabolic flux rely on macromolecules: large functionally diverse polymers of repeating units (nucleotides, amino acids). Regulatory mechanisms superimposed on these processes often rely on these very same kinds of macromolecules.

Nevertheless, recent studies have revealed a rich network of regulatory controls based on small molecules, and Grundy et al. now identify the L box, named for its involvement in lysine pathways. Lysine, in addition to being an essential amino acid, is used as a cross-linking building block (along with its precursor diaminopimelic acid) for the bacterial cell wall. The L box is an approximately 200-nucleotide region of the upstream portions of RNAs encoding lysine biosynthetic enzymes; in the presence of millimolar concentrations of lysine, its secondary structure changes and stops synthesis of the RNAs. Even though there is little sequence similarity between the L box of different genes, unlike the S box (which responds to S-adenosyl methionine levels), these sensors are alike in being able to discriminate between closely related metabolites (in this case, lysine versus diaminopimelic acid). — GJC

Proc. Natl. Acad. Sci. U.S.A. 100, 12057 (2003).

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