The Moco RNA motif is a conserved RNA structure that is involved in regulation of the molybdenum cofactor (Moco) and tungsten cofactor (Tuco) biosynthesis in diverse bacterial species. Moco is a cofactor required for the activity of several enzymes that mainly catalyze oxygen atom transfer reactions in the nitrogen, sulfur, and carbon metabolism . Molybdenum (Mo) and tungsten (W) are transition metals with very similar properties that are bound in proteins to a pterin cofactor, a heterocyclic compound synthesized from GTP.
The Moco RNA motif was originally identified by bioinformatics as a conserved RNA-like structure located upstream of genes encoding Mo transporters, Moco biosynthesis enzymes, and proteins that utilize Moco as a coenzyme .
Genetic experiments showed that a Moco RNA in Escherichia coli associated with the Moco biosynthetic operon controls gene expression in response to Moco production [18363797
]. In-line probing assays confirmed structural characteristics of a Moco RNA. Mutations in the Moco biosynthesis genes suggest that Moco is the regulatory ligand of the RNA.
These results, together with extensive phylogenetic conservation and typical gene control structures indicated that the Moco RNA element represents a novel class of riboswitches that sense Moco [18363797
]. As Moco cofactor is not available in purified form, in vitro binding assays was not yet performed.