tRNAHis is the specific tRNA that assists in incorporating the amino acid histidine into new proteins. Histidine residues make essential contributions to protein structure as well as the catalytic mechanisms of enzymes and must be reliably incorporated during the process of translation.
Until now, bacterial, archaeal, and eukaryotic tRNAs have always been found with an extra guanylate residue at the 5' end of the tRNA molecule. The scientists, led by Kelly Williams of VBI, have shown that tRNAs carrying the amino acid histidine in the alphaproteobacteria Sinorhizobium meliloti and Caulobacter crescentus apparently lack the universal guanylate residue.
Kelly Williams, research investigator at VBI, remarked: "The loss of a universal and apparently ancient tRNA feature in two members of the alphaproteobacteria was particularly surprising as it represents a radical departure from previously known identity rules for the histidine-carrying tRNAs." He added: "This result implies that tRNA recognition by the enzyme adding histidine to tRNA differs considerably from similar enzymes in other organisms. We have indeed been able to detect an impact on particular regions of the histidyl-tRNA synthetase that are critical for recognizing tRNA."
The researchers used bioinformatic tools such as a computer script ?specifically written by the group ?to probe the tRNA genes in the alphaproteobacteria group. Examination of the corrected tRNAHis sequences revealed that a group of alphaproteobacteria fails to encode a G (guanylate) at the -1 position of the tRNA