What happens to eIF2 when AUG is recognized during translation initiation?

When AUG is recognized during translation initiation, eIF2 (eukaryotic initiation factor 2) undergoes a crucial change. Specifically, eIF2, which carries the initiator methionyl-tRNA (Met-tRNAi), is bound to GTP in its active state. Upon recognition of the AUG start codon by the Met-tRNAi on the small ribosomal subunit, a conformational change occurs that triggers the hydrolysis of GTP to GDP.

This hydrolysis is a significant step because it not only activates the ribosome for the next steps in translation but also leads to a change in the affinity of eIF2. Once GTP is hydrolyzed to GDP, eIF2 becomes less stable and is more likely to be released from the ribosome. This process is critical for the proper assembly of the translation initiation complex, ensuring that translation begins accurately at the start codon.

The recognition of the AUG codon thus plays a key role in eIF2's function and the overall regulation of protein synthesis.