MnmC

MnmC is a bacterial enzyme involved in the post-transcriptional modification of uridine 34 (U34) at the wobble position of several tRNAs. It functions within the MnmE–MnmG (also known as GidA–MnmE) pathway that initiates formation of cmnm5U34 and carries out a final maturation step to mnm5s2U34, a modified uridine important for accurate codon recognition during translation. The enzyme is typically bifunctional, containing two domains known as MnmC1 and MnmC2, which act in sequence to convert cmnm5U34 into mnm5s2U34.

The MnmC1 domain is believed to perform oxidative processing of the cmnm moiety, producing an intermediate such as nm5U, while the MnmC2 domain functions as a methyltransferase to complete the formation of mnm5s2U. In many bacteria, these domains are encoded by the mnmC gene as a single polypeptide, though some organisms show variations in domain organization or separate subunits.

MnmC operates in coordination with MnmE and MnmG to influence the decoding properties of tRNAs, thereby affecting translation efficiency and fidelity under various growth and stress conditions. Disruption of mnmC can lead to altered tRNA modification patterns, potentially impacting growth and stress tolerance.

Research on MnmC has primarily focused on Escherichia coli and other bacteria, with structural and biochemical studies supporting the two-domain architecture and the sequential nature of its catalytic steps. Ongoing work aims to clarify the detailed mechanisms, substrate specificities, and broader physiological significance of MnmC across diverse bacterial species.