This subproject is one of many research subprojects utilizing the resources provided by a Center grant funded by NIH/NCRR. Primary support for the subproject and the subproject's principal investigator may have been provided by other sources, including other NIH sources. The Total Cost listed for the subproject likely represents the estimated amount of Center infrastructure utilized by the subproject, not direct funding provided by the NCRR grant to the subproject or subproject staff. Trbp111 is an ancient, structure-specific tRNA recognition domain found in many novel, human apoptosis-related cytokines, aminoacyl-tRNA synthetases, and other components of the protein synthesis apparatus. The function of this domain is to recognize the general L-shape of tRNA, regardless of sequence, and deliver it to its receptor enzyme for efficient aminoacylation. I want to understand the nature of this structure-specific tRNA recognition at an atomic level. Therefore, I determined the crystal structure of bacterial Trbp111 which revealed a homodimer with two OB-fold domains and a novel dimer interface (Swairjo et al., EMBO J, 19: 6287, 2000). I am now pursuing the crystal structure of the complex with tRNA. I have produced crystals of Aquifex aeolicus Trbp111 complexed with E. coli tRNAfMet which diffract to 7.0 ¿ on in-house equipment. I hope to collect higher-resolution X-ray data at SSRL that would allow for determination of the complex structure. This project is part of our general interest in studying several, novel, non-specific RNA recognition domains identified recently in genomic databases (Avarind and Koonin, J. Mol. Evol., 38: 291, 1999).