TRANSLATION OF TRPG IN BACILLUS-SUBTILIS IS REGULATED BY THE TRP RNA-BINDING ATTENUATION PROTEIN (TRAP)

trpG of Bacillus subtilis encodes a glutamine amidotransferase subunit that is involved in the synthesis of both folic acid and L-tryptophan . Expression of trpG is negatively regulated by tryptophan even though this gene is located within a folic acid biosynthetic operon. Examina tion of both transcriptional and translational gene fusions to lacZ in volving trpG and direct measurements of trpG mRNA levels and TrpG poly peptide accumulation demonstrated that translation of trpG is regulate d by tryptophan whereas transcription is not. These studies also show that this regulation is mediated by the trp RNA-binding attenuation pr otein. Deletion and point mutations indicated that regulation is depen dent on a series of G/UAG trinucleotide repeats surrounding the putati ve ribosome-binding site for trpG. Our results are consistent with a m odel in which the tryptophan-activated trp RNA-binding attenuation pro tein and ribosomes compete for binding to trpG mRNA.