Altered expression of plant lysyl tRNA synthetase promotes tRNA misacylation and translational recoding of lysine.

The Arabidopsis thaliana lysyl tRNA synthetase (AtKRS) structurally and functionally resembles the well-characterized prokaryotic class IIb KRS, including the propensity to aminoacylate tRNA(Lys) with suboptimal identity elements, as well as non-cognate tRNAs. Transient expression of AtKRS in carrot cells promotes aminoacylation of such tRNAs in vivo and translational recoding of lysine at nonsense codons. Stable expression of AtKRS in Zea mays causes translational recoding of lysine into zeins, significantly enriching the lysine content of grain.

Identity elements and aminoacylation of plant tRNATrp.

Mutation of the Arabidopsis thaliana tRNA (Trp)(CCA) anticodon or of the A73 discriminator base greatly diminishes in vitro aminoacylation with tryptophan, indicating the importance of these nucleotides for recognition by the plant tryptophanyl-tRNA synthetase. Mutation of the tRNA (Trp)(CCA) anticodon to CUA so as to translate amber nonsense codons permits tRNA (Trp)(CCA) to be aminoacylated by A.thaliana lysyl-tRNA synthetase.

The environment of 5S rRNA in the ribosome: cross-links to the GTPase-associated area of 23S rRNA.

Two photoreactive diazirine derivatives of uridine were used to study contacts between 5S rRNA and 23 rRNA in situ in Escherichia coli ribosomes. 2'-Amino-2'-deoxy-uridine or 5-methyleneaminouridine were introduced into 5S rRNA by T7 transcription. After incorporation of these uridine analogues into the transcript their amino groups were modified with 4-[3-(trifluoromethyl)-3 H -diazirin-3-yl]benzyl isothiocyanate or the N -hydroxysuccinimide ester of 4-[3-(trifluoromethyl)-3 H -diazirin-3-yl]benzoic acid respectively.

Opioid ligands with extraordinarily high mu-selectivity: dermorphin tetrapeptides containing thymine-modified alanine residues.

Four new [D-MetO2]dermorphin tetrapeptides with substituted N- and C-terminal groups and a thymine-modified alanine residue at position 4 were prepared and tested for their activity. All analogues were found to be mu-opioid receptor ligands. Two of them, H-Tyr-D-MetO-Phe-TalNHR (R = H, Ad) displayed an extremely high mu-opioid receptor selectivity comparable with that of the most mu-selective agonists among opioid peptides.