Question

If TRAP binds a read-through transcript, translation of the trpE gene is suppressed, how?

Answer 1

Answer )

The trp RNA-binding attenuation protein (TRAP) regulates expression of the tryptophan biosynthetic. TRAP consists of eleven identical subunits and is activated to bind RNA by binding up to eleven molecules of L-tryptophan. The TRAP binding site in the leader region of the trp operon mRNA consists of eleven (G/U)AG repeats.

Transcription of the trpEDCFBA operon is controlled by an attenuation mechanism involving two overlapping RNA secondary structures in the 5′ leader region of the trp transcript; TRAP binding promotes formation of a transcription terminator structure that halts transcription prior to the structural genes.Transcription of the trp operon is regulated by an attenuation mechanism that involves two mutually exclusive RNA secondary structures that can form in the 203 nucleotide  untranslated leader region 5′ to trpE. TRAP binding to the trp leader region of the nascent trp mRNA inhibits formation of the antiterminator thereby inducing formation of the terminator structure, which halts transcription prior to the structural genes.

Tryptophan binding activates TRAP to bind RNA, at least in part, by reducing the flexibility of the protein. TRAP binding sites contain multiple (up to 11) NAG repeats (N = G ≈ U > A > C) separated by several nonconserved “spacer” nucleotides. Several structures of TRAP complexed with RNAs composed of 11 GAG or 11 UAG repeats which bound to RNA wraps around the outside of the protein ring with the phosphodiester backbone exposed to the solution. The majority of the contacts between the protein and the RNA are to the bases of the AG portion of each (G/U)AG repeat, which interact with Glu36, Lys37, Lys56 and Agr58 of each TRAP subuniT