Many bacterial species recognize the amino acid tryptophan and its transfer RNA as a regulatory signal responsible for tryptophan biosynthesis. In September 14 Science, Angela Valbuzzi and Charles Yanofsky from the Department of Biological Sciences, Stanford University determined that, in addition to sensing the amount of tryptophan present, Bacillus subtilis also has a mechanism for detecting the concentration of tryptophan-specific tRNA.

Valbuzzi & Yanofsky discovered that if the amount of tryptophan-laden tRNA is low, a subset of B. subtilis genes begin producing the previously unknown protein anti-TRAP (AT). AT associates with TRAP, a trp operon attenuation protein, and inhibits TRAP binding to its target RNA sequences. This relieves TRAP-mediated transcription termination and translation inhibition and increases the rate of tryptophan biosynthesis (Science 2001, 293:2057-2059).

The mechanisms of regulation of expression of the genes of tryptophan biosynthesis in B. subtilis differ considerably from those used for instance by...

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