ИСТИНА

Different stages of a protein biosynthesis require particular states of the ribosomal complexes. To match this states an intrinsic mobility of the ribosome needs to be limited therefore a stabilization of the ribosomal complexes plays an important role in translational control. Mechanisms of the ribosome stabilization have been elucidated in details for initiation and elongation stages of eukaryotic translation, but the termination stage is poorly understood for that matter. We present one of the mechanisms of fine-tuning of the translation termination process in eukaryotes. We showed that certain deacylated tRNAs, remaining in the E site of the ribosome at the end of the elongation cycle, increased the stability of the termination and posttermination complexes. It is the acceptor stem of a deacylated tRNA that defines this property that was demonstrated with help of site-directed mutagenesis of tRNAVal and construction of a mini-helix structure identical to the tRNA acceptor stem. Only the part of termination factor eRF1 recognizing a stop codon is stabilized in the A site of the ribosome, and the effect is not dependent on the peptidyl-tRNA hydrolysis. The mechanism of this stabilization is different from the fixation of the unrotated state of the ribosome by CCA end of tRNA or by cycloheximide in the E site. Our data reveal the possible functions of the isodecoder tRNAs in eukaryotes.