QueF

queF is a gene encoding an enzyme in the bacterial and archaeal queuosine biosynthesis pathway. It represents a key step in converting a precursor molecule into the form used to generate queuosine, a modified nucleoside found in certain tRNAs.

Function and pathway context

The QueF enzyme specifically catalyzes the reduction of preQ0 (7-cyano-7-deazaguanine) to preQ1 (7-aminomethyl-7-deazaguanine), a necessary step before the mature queuosine structure is formed. This reaction is part of the queuosine biosynthesis sequence that starts from GTP and proceeds through several enzymes, including QueC, QueD, and QueE. After QueF acts, preQ1 is incorporated into tRNA by tRNA-guanine transglycosylase (TGT) in a process that ultimately yields queuosine at the wobble position of certain tRNAs.

Genomic distribution and regulation

queF is typically found in bacterial genomes and in some archaea, often as part of an operon that includes queC, queD, and queE. Its presence varies among organisms, and many eukaryotes do not synthesize queuosine de novo and instead salvage it from the diet or microbiome. The activity of QueF can influence the overall level of queuosine modification in tRNA and, by extension, translation under various conditions.

Structure and mechanism

QueF proteins are relatively small, usually around 90–110 amino acids, with a conserved active-site cysteine essential for catalysis. The enzyme commonly uses reducing equivalents from thioredoxin or NADPH, depending on the organism, to drive the reduction of preQ0 to preQ1.

Biological significance

Queuosine-modified tRNAs participate in accurate and efficient decoding at the ribosome, affecting codon-anticodon interactions for specific amino acids. Variations in QueF activity can impact bacterial growth, stress responses, and, in some pathogens, virulence traits, making the pathway a subject of interest in microbiology and antibiotic research.