Structure of the trp RNA-binding attenuation protein, TRAP, bound to RNA.
Antson, Alfred A. *; Dodson, Eleanor J. *; Dodson, Guy *; Greaves, Richard B. *; Chen, Xiao-ping +++; Gollnick, Paul +
[Article] Nature. 401(6750):235-242, September 16, 1999.

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The trp RNA-binding attenuation protein (TRAP) regulates expression of the tryptophan biosynthetic genes of several bacilli by binding single-stranded RNA. The binding sequence is composed of eleven triplet repeats, predominantly GAG, separated by two or three non-conserved nucleotides. Here we present the crystal structure of a complex of TRAP and a 53-base single-stranded RNA containing eleven GAG triplets, revealing that each triplet is accommodated in a binding pocket formed by [beta]-strands. In the complex, the RNA has an extended structure without any base-pairing and binds to the protein mostly by specific protein-base interactions. Eleven binding pockets on the circular TRAP 11-mer form a belt with a diameter of about 80 A. This simple but elegant mechanism of arresting the RNA segment by encircling it around a protein disk is applicable to both transcription, when TRAP binds the nascent RNA, and to translation, when TRAP binds the same sequence within a non-coding leader region of the messenger RNA.

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