queA

queA is the gene name for an enzyme called S-adenosylmethionine:tRNA ribosyltransferase-isomerase, involved in the biosynthesis of the modified nucleoside queuosine (Q) in tRNA. It is found in many bacteria and archaea that synthesize queuosine and is typically located within operons containing other queuosine biosynthesis genes such as queC, queD, queE, queF, and queG.

Biochemical function and pathway context: QueA catalyzes the transfer of a ribose moiety from S-adenosyl-L-methionine (SAM) to preQ1, a late precursor in queuosine biosynthesis, on the wobble position of certain tRNAs. The reaction produces an intermediate known as epoxyqueuosine-containing tRNA, which is subsequently reduced to queuosine by QueG or related enzymes. This combined transfer and rearrangement step is why QueA is described as a ribosyltransferase-isomerase.

Biological significance and distribution: Queuosine at the wobble position of tRNAs participates in codon-anticodon decoding and can influence translational accuracy and efficiency. In many bacteria and archaea, QueA activity is required for producing Q-containing tRNAs for tyrosine, asparagine, aspartate, and histidine codons. Eukaryotes generally lack de novo queuosine biosynthesis and obtain queuosine through diet or gut microbiota, relying more on salvage pathways rather than queA. In pathogenic bacteria, QueA and the queuosine biosynthesis operon can affect fitness, making them potential targets for antimicrobial strategies.