NTAQ1 (N-terminal glutamine amidase 1) is a monomeric enzyme that catalyzes the deamidation of N-terminal glutamine residues to glutamate, an initiating step in the arginine/N-degron protein degradation pathway 1. The enzyme contains a conserved catalytic triad (Cys-His-Asp) structurally similar to transglutaminases and cysteine proteases 2. NTAQ1 recognizes substrates primarily through N-terminal backbone interactions rather than side-chain specificity, with second-position residues modulating activity except proline, which abolishes deamidation 3. Deamidation converts N-terminal glutamine to glutamate, rendering proteins susceptible to arginylation by ATE1 and subsequent polyubiquitination by UBR1/UBR2 E3 ligases, targeting them for proteasomal degradation 4. NTAQ1 functions within a targeting complex with other N-degron pathway enzymes, enabling substrate channeling without dissociation into bulk solution 4. Physiologically, NTAQ1 regulates genomic stability by degrading the autocleaved Usp1 deubiquitylase fragment, controlling PCNA monoubiquitylation 5. Additionally, NTAQ1 processes ubiquitin variants, enabling N-terminal arginylation of ubiquitin that attaches to histone H2A, expanding histone ubiquitylation complexity 6. The enzyme is highly conserved across animals, plants, and fungi, indicating fundamental importance in protein regulation.