Crystallization and preliminary X-ray analysis of the mRNA-binding domain of elongation factor SelB in complex with RNA

In bacteria, the selenocysteine-specific elongation factor SelB is necessary for incorporation of selenocysteine, the 21st amino acid, into proteins by the ribosome. SelB binds to an mRNA hairpin formed by the selenocysteine-insertion sequence (SECIS) and delivers selenocysteyl-tRNA (Sec-tRNA^Sec) at the ribosomal A site. The minimum fragment (residues 512-634) of Moorella thermoacetica SelB (SelB-M) required for mRNA binding has been overexpressed and purified. The complex of SelB-M with 23 nucleotides of the SECIS mRNA hairpin was crystallized at 293 K using the hanging-drop vapour-diffusion or oil-batch methods. The crystals diffract to 2.3 Å resolution using SPring-8 BL41XU and belong to the space group P2 ₁2₁2, with unit-cell parameters a = 81.69, b = 169.58, c = 71.69 Å.