queC

QueC, or queuosine biosynthesis protein C, is an enzyme encoded by the queC gene and is involved in the biosynthesis of queuosine, a hypermodified guanine found at the wobble position of many bacterial tRNAs. Queuosine is believed to influence translation accuracy and efficiency. QueC is typically found in bacteria and some archaea and is usually co-located in an operon with queD and queE, which together supply late-stage precursors to the pathway.

Biochemical role: QueC is part of the queuosine biosynthesis pathway and is thought to participate in an ATP-dependent activation step that licenses conversion of a queuosine precursor into a downstream intermediate used by subsequent enzymes to generate preQ1 or related compounds. The exact substrates and chemical transformation are a subject of ongoing study, but activation of a reactive intermediate by QueC is widely proposed.

Protein characteristics: QueC proteins are typically around 25–35 kilodaltons and predicted to be cytosolic. Bioinformatic analyses place them in the PP-loop ATP pyrophosphatase family, sharing conserved motifs that bind ATP and the substrate.

Distribution and evolution: The presence of queC correlates with organisms that synthesize queuosine in tRNA. Phylogenetic analyses suggest horizontal transfer events and a broad vertical distribution across bacterial lineages; archaeal occurrences are comparatively rare.

Significance: Because queuosine modification is linked to translational control, QueC is of interest in studies of bacterial physiology and evolution. It also serves as a marker for pathways enabling queuosine biosynthesis and as a reference point in comparative genomics of tRNA modification systems.

See also: queuosine, queD, queE, queA, tgt (tRNA-guanine transglycosylase).