Loss of a universal tRNA feature

Virginia Bioinformatics Institute, Virginia Polytechnic Institute and State University, Blacksburg VA 24061

^* To whom correspondence should be addressed. Email: kellwill{at}vt.edu.

	Abstract

tRNA^His has always hitherto been found with one of the most distinctive of tRNA features, an extra 5 nucleotide that is usually a guanylate. tRNA^His genes in a disjoint alphaproteobacterial group comprising the Rhizobiales, Rhodobacterales, Caulobacterales, Parvularculales and Pelagibacter generally fail to encode this extra guanylate, unlike those of other alphaproteobacteria and bacteria in general. Rather than adding an extra 5 guanylate posttranscriptionally as eukaryotes do, evidence is presented that two of these species, Sinorhizobium meliloti and Caulobacter crescentus, simply lack any extra nucleotide on tRNA^His. This loss correlates with changes at the 3 end sequence of tRNA^His and at many sites in histidyl-tRNA synthetase that might be expected to affect tRNA^His recognition, in the flipping loop, the insertion domain, the anticodon-binding domain, and in the motif 2 loop. The altered tRNA charging system may have affected other tRNA charging systems in these bacteria; for example, a site in tRNA^Glu sequences was found to covary with tRNA^His among alphaproteobacteria.