Preparation of a crystallizable mRNA-binding fragment of Moorella thermoacetica elongation factor SelB.

SelB is a bacterial elongation factor required for the decoding of a UGA stop codon together with a specific mRNA hairpin to selenocysteine. In attempts to crystallize Moorella thermoacetica SelB, a proteolysis process occurred and crystals of a proteolytic fragment were observed. The crystals, which appeared after a year, contained a C-terminal 30 kDa fragment containing the mRNA-binding domain. This fragment was reproduced through recloning. Crystals diffracting to 2.7 A were obtained.