THE TRP RNA-BINDING ATTENUATION PROTEIN REGULATES TRPG SYNTHESIS BY BINDING TO THE TRPG RIBOSOME BINDING-SITE OF BACILLUS-SUBTILIS

The trpG gene of Bacillus subtilis encodes a glutamine amidotransferas e subunit which is involved in the biosynthesis of L-tryptophan and fo lic acid, The trp RNA-binding attenuation protein (TRAP) is involved i n controlling expression of trpG at the level of translation in respon se to changes in the intracellular concentration of tryptophan. We per formed in vitro experiments using purified TRAP to elucidate the mecha nism of TRAP-dependent trpG regulation. A TRAP-trpG RNA footprint anal ysis showed that tryptophan-activated TRAP interacts with one UAG, one AAG, and seven GAG repeats present in the trpG transcript. Results fr om ribosome and TRAP toeprint experiments indicated that the ribosome and TRAP binding sites overlap. Experiments with a B. subtilis cell-fr ee translation system demonstrated that TRAP inhibits TrpG synthesis, Thus, TRAP regulates translation of trpG by blocking ribosome access t o the trpG ribosome binding site, Our results are consistent with a mo del in which each tryptophan-activated TRAP subunit interacts with one trinucleotide repeat in an RNA target, thereby wrapping the transcrip t around the periphery of the TRAP complex.