The KRAS G12A Nucleotide Exchange Assay Kit is a TR-FRET–based assay designed to measure the nucleotide exchange activity of the KRAS G12A mutant protein. KRAS is a small GTPase involved in Ras signaling pathways that regulate cell growth, proliferation, and differentiation. Mutations such as G12A reduce GTPase activity and maintain KRAS in an active GTP-bound state, contributing to cancer progression. In this assay, Tag2-KRAS G12A is recognized by a terbium-labeled anti-Tag2 antibody (HTRF donor). Binding of fluorescently labeled GTP (HTRF acceptor) brings donor and acceptor into close proximity, enabling FRET upon excitation at 340 nm and emission at 665 nm. The fluorescence ratio (665/620 nm) quantitatively reflects GTP binding activity. Compounds that inhibit nucleotide exchange reduce the HTRF signal, making the kit suitable for screening KRAS G12A inhibitors.