The trp RNA-binding attenuation protein (TRAP) of B. subtilis consists of 11 subunits, each capable of binding one molecule of tryptophan.

When saturated with tryptophan, TRAP can bind to the 5'-leader sequence of the mRNA, forming a terminator hairpin and lead to attenuation of expression of the trp operon.

If tryptophan is scarce, an anti-TRAP (AT) protein inhibits binding of TRAP to the leader sequence, stopping the attenuation.